Is it ever okay to use lists in a relational database?











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I've been trying to design a database to go with a project concept and ran into what seems like a hotly debated issue. I've read a few articles and some Stack Overflow answers that state it's never (or almost never) okay to store a list of IDs or the like in a field -- all data should be relational, etc.



The problem I'm running into, though, is that I'm trying to make a task assigner. People will create tasks, assign them to multiple people, and it will save to the database.



Of course, if I save these tasks individually in "Person", I'll have to have dozens of dummy "TaskID" columns and micro-manage them because there can be 0 to 100 tasks assigned to one person, say.



Then again, if I save the tasks in a "Tasks" table, I'll have to have dozens of dummy "PersonID" columns and micro-manage them -- same problem as before.



For a problem like this, is it okay to save a list of IDs taking one form or another or am I just not thinking of another way this is achievable without breaking principles?










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  • 16




    I realize this is tagged "relational database" so I'll just leave it as a comment not an answer, but in other types of databases it does make sense to store lists. Cassandra comes to mind since it has no joins.
    – Captain Man
    2 days ago






  • 6




    Good job in researching and then asking here! Indeed, the 'recommendation' to never violate the 1st normal form did really well for you, because you really should come up with another, relational approach, namely a "many-to-many" relation, for which there is a standard pattern in relational databases which should be used.
    – JimmyB
    yesterday








  • 1




    "Is it ever okay" yes.... whatever follows, the answer is yes. As long as you have a valid reason. There's always a use case that compels you to violate best practices because it makes sense to do so. (In your case, though, you definitely shouldn't)
    – xyious
    22 hours ago










  • Totally agree with xyious on this one. The one time I've stored a delimited list of ints in a database table was when I didn't need to do anything with this list inside the database - only to store and retrieve it - and therefor it made sense to store it as a list. But that's a single incident over a professional programming career that spans over two decades, so you can understand it's a rare case.
    – Zohar Peled
    21 hours ago










  • I'm currently using an array (not a delimited string -- a VARCHAR ARRAY) to store a list of tags. That's probably not how they'll end up being stored later down the line, but lists can be extremely useful during the prototyping stages, when you have nothing else to point to and don't want to build out the entire database schema before you can do anything else.
    – Nic Hartley
    19 hours ago















up vote
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down vote

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I've been trying to design a database to go with a project concept and ran into what seems like a hotly debated issue. I've read a few articles and some Stack Overflow answers that state it's never (or almost never) okay to store a list of IDs or the like in a field -- all data should be relational, etc.



The problem I'm running into, though, is that I'm trying to make a task assigner. People will create tasks, assign them to multiple people, and it will save to the database.



Of course, if I save these tasks individually in "Person", I'll have to have dozens of dummy "TaskID" columns and micro-manage them because there can be 0 to 100 tasks assigned to one person, say.



Then again, if I save the tasks in a "Tasks" table, I'll have to have dozens of dummy "PersonID" columns and micro-manage them -- same problem as before.



For a problem like this, is it okay to save a list of IDs taking one form or another or am I just not thinking of another way this is achievable without breaking principles?










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  • 16




    I realize this is tagged "relational database" so I'll just leave it as a comment not an answer, but in other types of databases it does make sense to store lists. Cassandra comes to mind since it has no joins.
    – Captain Man
    2 days ago






  • 6




    Good job in researching and then asking here! Indeed, the 'recommendation' to never violate the 1st normal form did really well for you, because you really should come up with another, relational approach, namely a "many-to-many" relation, for which there is a standard pattern in relational databases which should be used.
    – JimmyB
    yesterday








  • 1




    "Is it ever okay" yes.... whatever follows, the answer is yes. As long as you have a valid reason. There's always a use case that compels you to violate best practices because it makes sense to do so. (In your case, though, you definitely shouldn't)
    – xyious
    22 hours ago










  • Totally agree with xyious on this one. The one time I've stored a delimited list of ints in a database table was when I didn't need to do anything with this list inside the database - only to store and retrieve it - and therefor it made sense to store it as a list. But that's a single incident over a professional programming career that spans over two decades, so you can understand it's a rare case.
    – Zohar Peled
    21 hours ago










  • I'm currently using an array (not a delimited string -- a VARCHAR ARRAY) to store a list of tags. That's probably not how they'll end up being stored later down the line, but lists can be extremely useful during the prototyping stages, when you have nothing else to point to and don't want to build out the entire database schema before you can do anything else.
    – Nic Hartley
    19 hours ago













up vote
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up vote
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down vote

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I've been trying to design a database to go with a project concept and ran into what seems like a hotly debated issue. I've read a few articles and some Stack Overflow answers that state it's never (or almost never) okay to store a list of IDs or the like in a field -- all data should be relational, etc.



The problem I'm running into, though, is that I'm trying to make a task assigner. People will create tasks, assign them to multiple people, and it will save to the database.



Of course, if I save these tasks individually in "Person", I'll have to have dozens of dummy "TaskID" columns and micro-manage them because there can be 0 to 100 tasks assigned to one person, say.



Then again, if I save the tasks in a "Tasks" table, I'll have to have dozens of dummy "PersonID" columns and micro-manage them -- same problem as before.



For a problem like this, is it okay to save a list of IDs taking one form or another or am I just not thinking of another way this is achievable without breaking principles?










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linus72982 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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I've been trying to design a database to go with a project concept and ran into what seems like a hotly debated issue. I've read a few articles and some Stack Overflow answers that state it's never (or almost never) okay to store a list of IDs or the like in a field -- all data should be relational, etc.



The problem I'm running into, though, is that I'm trying to make a task assigner. People will create tasks, assign them to multiple people, and it will save to the database.



Of course, if I save these tasks individually in "Person", I'll have to have dozens of dummy "TaskID" columns and micro-manage them because there can be 0 to 100 tasks assigned to one person, say.



Then again, if I save the tasks in a "Tasks" table, I'll have to have dozens of dummy "PersonID" columns and micro-manage them -- same problem as before.



For a problem like this, is it okay to save a list of IDs taking one form or another or am I just not thinking of another way this is achievable without breaking principles?







database database-design sql relational-database






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  • 16




    I realize this is tagged "relational database" so I'll just leave it as a comment not an answer, but in other types of databases it does make sense to store lists. Cassandra comes to mind since it has no joins.
    – Captain Man
    2 days ago






  • 6




    Good job in researching and then asking here! Indeed, the 'recommendation' to never violate the 1st normal form did really well for you, because you really should come up with another, relational approach, namely a "many-to-many" relation, for which there is a standard pattern in relational databases which should be used.
    – JimmyB
    yesterday








  • 1




    "Is it ever okay" yes.... whatever follows, the answer is yes. As long as you have a valid reason. There's always a use case that compels you to violate best practices because it makes sense to do so. (In your case, though, you definitely shouldn't)
    – xyious
    22 hours ago










  • Totally agree with xyious on this one. The one time I've stored a delimited list of ints in a database table was when I didn't need to do anything with this list inside the database - only to store and retrieve it - and therefor it made sense to store it as a list. But that's a single incident over a professional programming career that spans over two decades, so you can understand it's a rare case.
    – Zohar Peled
    21 hours ago










  • I'm currently using an array (not a delimited string -- a VARCHAR ARRAY) to store a list of tags. That's probably not how they'll end up being stored later down the line, but lists can be extremely useful during the prototyping stages, when you have nothing else to point to and don't want to build out the entire database schema before you can do anything else.
    – Nic Hartley
    19 hours ago














  • 16




    I realize this is tagged "relational database" so I'll just leave it as a comment not an answer, but in other types of databases it does make sense to store lists. Cassandra comes to mind since it has no joins.
    – Captain Man
    2 days ago






  • 6




    Good job in researching and then asking here! Indeed, the 'recommendation' to never violate the 1st normal form did really well for you, because you really should come up with another, relational approach, namely a "many-to-many" relation, for which there is a standard pattern in relational databases which should be used.
    – JimmyB
    yesterday








  • 1




    "Is it ever okay" yes.... whatever follows, the answer is yes. As long as you have a valid reason. There's always a use case that compels you to violate best practices because it makes sense to do so. (In your case, though, you definitely shouldn't)
    – xyious
    22 hours ago










  • Totally agree with xyious on this one. The one time I've stored a delimited list of ints in a database table was when I didn't need to do anything with this list inside the database - only to store and retrieve it - and therefor it made sense to store it as a list. But that's a single incident over a professional programming career that spans over two decades, so you can understand it's a rare case.
    – Zohar Peled
    21 hours ago










  • I'm currently using an array (not a delimited string -- a VARCHAR ARRAY) to store a list of tags. That's probably not how they'll end up being stored later down the line, but lists can be extremely useful during the prototyping stages, when you have nothing else to point to and don't want to build out the entire database schema before you can do anything else.
    – Nic Hartley
    19 hours ago








16




16




I realize this is tagged "relational database" so I'll just leave it as a comment not an answer, but in other types of databases it does make sense to store lists. Cassandra comes to mind since it has no joins.
– Captain Man
2 days ago




I realize this is tagged "relational database" so I'll just leave it as a comment not an answer, but in other types of databases it does make sense to store lists. Cassandra comes to mind since it has no joins.
– Captain Man
2 days ago




6




6




Good job in researching and then asking here! Indeed, the 'recommendation' to never violate the 1st normal form did really well for you, because you really should come up with another, relational approach, namely a "many-to-many" relation, for which there is a standard pattern in relational databases which should be used.
– JimmyB
yesterday






Good job in researching and then asking here! Indeed, the 'recommendation' to never violate the 1st normal form did really well for you, because you really should come up with another, relational approach, namely a "many-to-many" relation, for which there is a standard pattern in relational databases which should be used.
– JimmyB
yesterday






1




1




"Is it ever okay" yes.... whatever follows, the answer is yes. As long as you have a valid reason. There's always a use case that compels you to violate best practices because it makes sense to do so. (In your case, though, you definitely shouldn't)
– xyious
22 hours ago




"Is it ever okay" yes.... whatever follows, the answer is yes. As long as you have a valid reason. There's always a use case that compels you to violate best practices because it makes sense to do so. (In your case, though, you definitely shouldn't)
– xyious
22 hours ago












Totally agree with xyious on this one. The one time I've stored a delimited list of ints in a database table was when I didn't need to do anything with this list inside the database - only to store and retrieve it - and therefor it made sense to store it as a list. But that's a single incident over a professional programming career that spans over two decades, so you can understand it's a rare case.
– Zohar Peled
21 hours ago




Totally agree with xyious on this one. The one time I've stored a delimited list of ints in a database table was when I didn't need to do anything with this list inside the database - only to store and retrieve it - and therefor it made sense to store it as a list. But that's a single incident over a professional programming career that spans over two decades, so you can understand it's a rare case.
– Zohar Peled
21 hours ago












I'm currently using an array (not a delimited string -- a VARCHAR ARRAY) to store a list of tags. That's probably not how they'll end up being stored later down the line, but lists can be extremely useful during the prototyping stages, when you have nothing else to point to and don't want to build out the entire database schema before you can do anything else.
– Nic Hartley
19 hours ago




I'm currently using an array (not a delimited string -- a VARCHAR ARRAY) to store a list of tags. That's probably not how they'll end up being stored later down the line, but lists can be extremely useful during the prototyping stages, when you have nothing else to point to and don't want to build out the entire database schema before you can do anything else.
– Nic Hartley
19 hours ago










8 Answers
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The key word and key concept you need to investigate is database normalization.



What you would do, is rather than adding info about the assignments to the person or tasks tables, is you add a new table with that assignment info, with relevant relationships.



Example, you have the following tables:



Persons:



+----+-----------+
| ID | Name |
+====+===========+
| 1 | Alfred |
| 2 | Jebediah |
| 3 | Jacob |
| 4 | Ezekiel |
+----+-----------+


Tasks:



+----+--------------------+
| ID | Name |
+====+====================+
| 1 | Feed the Chickens |
| 2 | Plow |
| 3 | Milking Cows |
| 4 | Raise a barn |
+----+--------------------+


You would then create a third table with Assignments. This table would model the relationship between the people and the tasks:



+----+-----------+---------+
| ID | PersonId | TaskId |
+====+===========+=========+
| 1 | 1 | 3 |
| 2 | 3 | 2 |
| 3 | 2 | 1 |
| 4 | 1 | 4 |
+----+-----------+---------+


We would then have a Foreign Key constraint, such that the database will enforce that the PersonId and TaskIds have to be valid IDs for those foreign items. For the first row, we can see PersonId is 1, so Alfred, is assigned to TaskId 3, Milking cows.



What you should be able to see here is that you could have as few or as many assignments per task or per person as you want. In this example, Ezekiel isn't assigned any tasks, and Alfred is assigned 2. If you have one task with 100 people, doing SELECT PersonId from Assignments WHERE TaskId=<whatever>; will yield 100 rows, with a variety of different Persons assigned. You can WHERE on the PersonId to find all of the tasks assigned to that person.



If you want to return queries replacing the Ids with the Names and the tasks, then you get to learn how to JOIN tables.





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  • 45




    @linus72982: your assumption is correct, this is indeed a standard technique in database design for modelling N:M relationships. Unfortunately, it does not have a standard name, it's called "association table", "junction table", "join table", and probably a few other names as well.
    – Michael Borgwardt
    2 days ago






  • 59




    The keyword you want to search to learn more is "many-to-many relationship"
    – BlueRaja - Danny Pflughoeft
    2 days ago








  • 22




    To elaborate a little on Thierrys comment: You may think that you do not need to normalize because I only need X and it is very simple to store the ID list, but for any system that may get extended later you will regret not having normalized it earlier. Always normalize; the only question is to what normal form
    – Jan Doggen
    2 days ago








  • 5




    @Deduplicator: it's just a representation of a garden-variety, auto-increment integer primary key column. Pretty typical stuff.
    – whatsisname
    yesterday








  • 16




    I see what you did there.
    – Mac
    yesterday


















up vote
25
down vote













You're asking two questions here.



First, you ask if its ok to store lists serialized in a column. Yes, its fine. If your project calls for it. An example might be product ingredients for a catalog page, where you have no desire to try to track each ingredient individually.



Unfortunately your second question describes a scenario where you should opt for a more relational approach. You'll need 3 tables. One for the people, one for the tasks, and one that maintains the list of which task is assigned to which people. That last one would be vertical, one row per person/task combination, with columns for your primary key, task id, and person id.






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  • 8




    The ingredient example you reference is correct on the surface; but it would be plaintext in that case. It is not a list in the programming sense (unless you mean that the string is a list of characters which you obviously don't). OP describing their data as "a list of IDs" (or even just "a list of [..]") implies that they are at some point handling this data as individual objects.
    – Flater
    2 days ago








  • 6




    @Flater: But it is a list. You need to be able to reformat it as (variously) an HTML list, a Markdown list, a JSON list, etc. in order to ensure the items are displayed properly in (variously) a web page, a plain text document, a mobile app... and you can't really do that with plain text.
    – Kevin
    yesterday








  • 7




    @Kevin If that is your goal, then it is much more readily and easily achieved by storing the ingredients in a table! Not to mention if, later, people would ... oh, I don't know, say, wish for recommended substitutes, or something silly like look for all recipes without any peanuts, or gluten, or animal proteins...
    – Dan Bron
    yesterday








  • 7




    @DanBron: YAGNI. Right now we're only using a list because it makes the UI logic easier. If we need or will need list-like behavior in the business logic layer, then it should be normalized into a separate table. Tables and joins are not necessarily expensive, but they're not free, and they bring in questions about element order ("Do we care about the order of ingredients?") and further normalization ("Are you going to turn '3 eggs' into ('eggs', 3)? What about 'Salt, to taste', is that ('salt', NULL)?").
    – Kevin
    yesterday








  • 3




    @Kevin: YAGNI is quite wrong here. You yourself argued the necessity of being able to transform the list in many ways (HTML, markdown, JSON) and thus are arguing that you need the individual elements of the list. Unless the data storage and "list handling" applications are two applications that are developed independently (and do note that separate application layers != separate applications), the database structure should always be created to store the data in a format that leaves it readily available - while avoiding additional parsing/conversion logic.
    – Flater
    yesterday




















up vote
14
down vote













What you're describing is known as a "many to many" relationship, in your case between Person and Task. It's typically implemented using a third table, sometimes called a "link" or "cross-reference" table. For example:



create table person (
person_id integer primary key,
...
);

create table task (
task_id integer primary key,
...
);

create table person_task_xref (
person_id integer not null,
task_id integer not null,
primary key (person_id, task_id),
foreign key (person_id) references person (person_id),
foreign key (task_id) references task (task_id)
);





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    up vote
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    down vote














    ... it's never (or almost never) okay to store a list of IDs or the like in a field




    The only time you might store more than one data item in a single field is when that field is only ever used as a single entity and is never considered as being made up of those smaller elements. An example might be an image, stored in a BLOB field. It's made up of lots and lots of smaller elements (bytes) but these that mean nothing to the database and can only be used all together (and look pretty to an End User).



    Since a "list" is, by definition, made up of smaller elements (items), this isn't the case here and you should normalise the data.




    ... if I save these tasks individually in "Person", I'll have to have dozens of dummy "TaskID" columns ...




    No. You'll have a few rows in an Intersection Table (a.k.a. Weak Entity) between Person and Task. Databases are really good at working with lots of rows; they're actually pretty rubbish at working with lots of [repeated] columns.



    Nice clear example given by whatsisname.






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    • 1




      When creating real life systems "never say never" is a very good rule to live by.
      – l0b0
      yesterday


















    up vote
    2
    down vote













    It may be legitimate in certain pre-calculated fields.



    If some of your queries are expensive and you decide to go with pre-calculated fields updated automatically using database triggers, then it may be legitimate to keep the lists inside a column.



    For example, in the UI you want to show this list using grid view, where each row can open full details (with complete lists) after double-clicking:



    REGISTERED USER LIST
    +------------------+----------------------------------------------------+
    |Name |Top 3 most visited tags |
    +==================+====================================================+
    |Peter |Design, Fitness, Gifts |
    +------------------+----------------------------------------------------+
    |Lucy |Fashion, Gifts, Lifestyle |
    +------------------+----------------------------------------------------+


    You are keeping the second column updated by trigger when client visits new article or by scheduled task.



    You can make such a field available even for searching (as normal text).



    For such cases, keeping lists is legitimate. You just need to consider case of possibly exceeding maximum field length.





    Also, if you are using Microsoft Access, offered multivalued fields are another special use case. They handle your lists in a field automatically.



    But you can always fall back to standard normalized form shown in other answers.





    Summary: Normal forms of database are theoretical model required for understanding important aspects of data modeling. But of course normalization does not take into account performance or other cost of retrieving the data. It is out of scope of that theoretical model. But storing lists or other pre-calculated (and controlled) duplicates is often required by practical implementation.



    In the light of the above, in practical implementation, would we prefer query relying on perfect normal form and running 20 seconds or equivalent query relying on pre-calculated values which takes 0.08 s? No one likes their software product to be accused of slowness.






    share|improve this answer



















    • 1




      It can be legitimate even without precalculated stuff. I've done it a couple of times where the data is stored properly but for performance reasons it's useful to stuff a few cached results in the main records.
      – Loren Pechtel
      yesterday










    • @LorenPechtel – Yes, thanks, in my use of term pre-calculated I also include cases of cached values stored where needed. In systems with complex dependencies, they are the way to keep the performance normal. And if programmed with adequate know-how, these values are reliable and always-in-sync. I just did not want to add case of caching into the answer to keep the answer simple and on safe side. It got downvoted anyway. :)
      – miroxlav
      yesterday




















    up vote
    0
    down vote













    Given two tables; we'll call them Person and Task, each with it's own ID (PersonID, TaskID)... the basic idea is to create a third table to bind them together. We'll call this table PersonToTask. At the minimum it should have it's own ID, as well as the two others
    So when it comes to assigning someone to a task; you will no longer need to UPDATE the Person table, you just need to INSERT a new line into the PersonToTaskTable.
    And maintenance becomes easier- need to delete a task just becomes a DELETE based on TaskID, no more updating the Person table and it's associated parsing



    CREATE TABLE dbo.PersonToTask (
    pttID INT IDENTITY(1,1) NOT NULL,
    PersonID INT NULL,
    TaskID INT NULL
    )

    CREATE PROCEDURE dbo.Task_Assigned (@PersonID INT, @TaskID INT)
    AS
    BEGIN
    INSERT PersonToTask (PersonID, TaskID)
    VALUES (@PersonID, @TaskID)
    END

    CREATE PROCEDURE dbo.Task_Deleted (@TaskID INT)
    AS
    BEGIN
    DELETE PersonToTask WHERE TaskID = @TaskID
    DELETE Task WHERE TaskID = @TaskID
    END


    How about a simple report or who's all assigned to a task?



    CREATE PROCEDURE dbo.Task_CurrentAssigned (@TaskID INT)
    AS
    BEGIN
    SELECT PersonName
    FROM dbo.Person
    WHERE PersonID IN (SELECT PersonID FROM dbo.PersonToTask WHERE TaskID = @TaskID)
    END


    You of course could do a lot more; a TimeReport could be done if you added DateTime fields for TaskAssigned and TaskCompleted. It's all up to you






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      It may work if say you have human readable Primary keys and want a list of task #'s without having to deal with vertical nature of a table structure. i.e. much easier to read first table.



      ------------------------  
      Employee Name | Task
      Jack | 1,2,5
      Jill | 4,6,7
      ------------------------

      ------------------------
      Employee Name | Task
      Jack | 1
      Jack | 2
      Jack | 5
      Jill | 4
      Jill | 6
      Jill | 7
      ------------------------


      The question would then be: should the task list be stored or generated on demand, which largely would depend on requirements such as: how often the list are needed, how accurate how many data rows exist, how the data will be used, etc... after which analyzing the trade offs to user experience and meeting requirements should be done.



      For example comparing the time it would take to recall the 2 rows vs running a query that would generate the 2 rows. If it takes long and the user does not need the most up to date list(*expecting less than 1 change per day) then it could be stored.



      Or if the user needs a historical record of tasks assigned to them it would also make sense if the list was stored. So it really depends on what you are doing, never say never.






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      • As you say, it all depends on how the data is to be retrieved. If you /only/ ever query this table by User Name, then the "list" field is perfectly adequate. However, how can you query such a table to find out who is working on Task #1234567 and still keep it performant? Just about every kind of "find-X-anywhere-in-the-field" String function will cause such a query to /Table Scan/, slowing things to a crawl. With properly normalised, properly indexed data, that just doesn't happen.
        – Phill W.
        yesterday


















      up vote
      0
      down vote













      You're taking what should be another table, turning it through 90 degrees and shoehorning it into another table.



      It's like having an order table where you have itemProdcode1, itemQuantity1, itemPrice1 ... itemProdcode37, itemQuantity37, itemPrice37. Apart from being awkward to handle programmatically you can guarantee that tomorrow someone will want to order 38 things.



      I'd only do it your way if the 'list' isn't really a list, i.e. where it stands as a whole and each individual line item doesn't refer to some clear and independent entity. In that case just stuff it all in some data type that's big enough.



      So an order is a list, a Bill Of Materials is a list (or a list of lists, which would be even more of a nightmare to implement "sideways"). But a note/comment and a poem aren't.






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        protected by gnat yesterday



        Thank you for your interest in this question.
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        8 Answers
        8






        active

        oldest

        votes








        8 Answers
        8






        active

        oldest

        votes









        active

        oldest

        votes






        active

        oldest

        votes








        up vote
        190
        down vote



        accepted










        The key word and key concept you need to investigate is database normalization.



        What you would do, is rather than adding info about the assignments to the person or tasks tables, is you add a new table with that assignment info, with relevant relationships.



        Example, you have the following tables:



        Persons:



        +----+-----------+
        | ID | Name |
        +====+===========+
        | 1 | Alfred |
        | 2 | Jebediah |
        | 3 | Jacob |
        | 4 | Ezekiel |
        +----+-----------+


        Tasks:



        +----+--------------------+
        | ID | Name |
        +====+====================+
        | 1 | Feed the Chickens |
        | 2 | Plow |
        | 3 | Milking Cows |
        | 4 | Raise a barn |
        +----+--------------------+


        You would then create a third table with Assignments. This table would model the relationship between the people and the tasks:



        +----+-----------+---------+
        | ID | PersonId | TaskId |
        +====+===========+=========+
        | 1 | 1 | 3 |
        | 2 | 3 | 2 |
        | 3 | 2 | 1 |
        | 4 | 1 | 4 |
        +----+-----------+---------+


        We would then have a Foreign Key constraint, such that the database will enforce that the PersonId and TaskIds have to be valid IDs for those foreign items. For the first row, we can see PersonId is 1, so Alfred, is assigned to TaskId 3, Milking cows.



        What you should be able to see here is that you could have as few or as many assignments per task or per person as you want. In this example, Ezekiel isn't assigned any tasks, and Alfred is assigned 2. If you have one task with 100 people, doing SELECT PersonId from Assignments WHERE TaskId=<whatever>; will yield 100 rows, with a variety of different Persons assigned. You can WHERE on the PersonId to find all of the tasks assigned to that person.



        If you want to return queries replacing the Ids with the Names and the tasks, then you get to learn how to JOIN tables.





        share



















        • 45




          @linus72982: your assumption is correct, this is indeed a standard technique in database design for modelling N:M relationships. Unfortunately, it does not have a standard name, it's called "association table", "junction table", "join table", and probably a few other names as well.
          – Michael Borgwardt
          2 days ago






        • 59




          The keyword you want to search to learn more is "many-to-many relationship"
          – BlueRaja - Danny Pflughoeft
          2 days ago








        • 22




          To elaborate a little on Thierrys comment: You may think that you do not need to normalize because I only need X and it is very simple to store the ID list, but for any system that may get extended later you will regret not having normalized it earlier. Always normalize; the only question is to what normal form
          – Jan Doggen
          2 days ago








        • 5




          @Deduplicator: it's just a representation of a garden-variety, auto-increment integer primary key column. Pretty typical stuff.
          – whatsisname
          yesterday








        • 16




          I see what you did there.
          – Mac
          yesterday















        up vote
        190
        down vote



        accepted










        The key word and key concept you need to investigate is database normalization.



        What you would do, is rather than adding info about the assignments to the person or tasks tables, is you add a new table with that assignment info, with relevant relationships.



        Example, you have the following tables:



        Persons:



        +----+-----------+
        | ID | Name |
        +====+===========+
        | 1 | Alfred |
        | 2 | Jebediah |
        | 3 | Jacob |
        | 4 | Ezekiel |
        +----+-----------+


        Tasks:



        +----+--------------------+
        | ID | Name |
        +====+====================+
        | 1 | Feed the Chickens |
        | 2 | Plow |
        | 3 | Milking Cows |
        | 4 | Raise a barn |
        +----+--------------------+


        You would then create a third table with Assignments. This table would model the relationship between the people and the tasks:



        +----+-----------+---------+
        | ID | PersonId | TaskId |
        +====+===========+=========+
        | 1 | 1 | 3 |
        | 2 | 3 | 2 |
        | 3 | 2 | 1 |
        | 4 | 1 | 4 |
        +----+-----------+---------+


        We would then have a Foreign Key constraint, such that the database will enforce that the PersonId and TaskIds have to be valid IDs for those foreign items. For the first row, we can see PersonId is 1, so Alfred, is assigned to TaskId 3, Milking cows.



        What you should be able to see here is that you could have as few or as many assignments per task or per person as you want. In this example, Ezekiel isn't assigned any tasks, and Alfred is assigned 2. If you have one task with 100 people, doing SELECT PersonId from Assignments WHERE TaskId=<whatever>; will yield 100 rows, with a variety of different Persons assigned. You can WHERE on the PersonId to find all of the tasks assigned to that person.



        If you want to return queries replacing the Ids with the Names and the tasks, then you get to learn how to JOIN tables.





        share



















        • 45




          @linus72982: your assumption is correct, this is indeed a standard technique in database design for modelling N:M relationships. Unfortunately, it does not have a standard name, it's called "association table", "junction table", "join table", and probably a few other names as well.
          – Michael Borgwardt
          2 days ago






        • 59




          The keyword you want to search to learn more is "many-to-many relationship"
          – BlueRaja - Danny Pflughoeft
          2 days ago








        • 22




          To elaborate a little on Thierrys comment: You may think that you do not need to normalize because I only need X and it is very simple to store the ID list, but for any system that may get extended later you will regret not having normalized it earlier. Always normalize; the only question is to what normal form
          – Jan Doggen
          2 days ago








        • 5




          @Deduplicator: it's just a representation of a garden-variety, auto-increment integer primary key column. Pretty typical stuff.
          – whatsisname
          yesterday








        • 16




          I see what you did there.
          – Mac
          yesterday













        up vote
        190
        down vote



        accepted







        up vote
        190
        down vote



        accepted






        The key word and key concept you need to investigate is database normalization.



        What you would do, is rather than adding info about the assignments to the person or tasks tables, is you add a new table with that assignment info, with relevant relationships.



        Example, you have the following tables:



        Persons:



        +----+-----------+
        | ID | Name |
        +====+===========+
        | 1 | Alfred |
        | 2 | Jebediah |
        | 3 | Jacob |
        | 4 | Ezekiel |
        +----+-----------+


        Tasks:



        +----+--------------------+
        | ID | Name |
        +====+====================+
        | 1 | Feed the Chickens |
        | 2 | Plow |
        | 3 | Milking Cows |
        | 4 | Raise a barn |
        +----+--------------------+


        You would then create a third table with Assignments. This table would model the relationship between the people and the tasks:



        +----+-----------+---------+
        | ID | PersonId | TaskId |
        +====+===========+=========+
        | 1 | 1 | 3 |
        | 2 | 3 | 2 |
        | 3 | 2 | 1 |
        | 4 | 1 | 4 |
        +----+-----------+---------+


        We would then have a Foreign Key constraint, such that the database will enforce that the PersonId and TaskIds have to be valid IDs for those foreign items. For the first row, we can see PersonId is 1, so Alfred, is assigned to TaskId 3, Milking cows.



        What you should be able to see here is that you could have as few or as many assignments per task or per person as you want. In this example, Ezekiel isn't assigned any tasks, and Alfred is assigned 2. If you have one task with 100 people, doing SELECT PersonId from Assignments WHERE TaskId=<whatever>; will yield 100 rows, with a variety of different Persons assigned. You can WHERE on the PersonId to find all of the tasks assigned to that person.



        If you want to return queries replacing the Ids with the Names and the tasks, then you get to learn how to JOIN tables.





        share














        The key word and key concept you need to investigate is database normalization.



        What you would do, is rather than adding info about the assignments to the person or tasks tables, is you add a new table with that assignment info, with relevant relationships.



        Example, you have the following tables:



        Persons:



        +----+-----------+
        | ID | Name |
        +====+===========+
        | 1 | Alfred |
        | 2 | Jebediah |
        | 3 | Jacob |
        | 4 | Ezekiel |
        +----+-----------+


        Tasks:



        +----+--------------------+
        | ID | Name |
        +====+====================+
        | 1 | Feed the Chickens |
        | 2 | Plow |
        | 3 | Milking Cows |
        | 4 | Raise a barn |
        +----+--------------------+


        You would then create a third table with Assignments. This table would model the relationship between the people and the tasks:



        +----+-----------+---------+
        | ID | PersonId | TaskId |
        +====+===========+=========+
        | 1 | 1 | 3 |
        | 2 | 3 | 2 |
        | 3 | 2 | 1 |
        | 4 | 1 | 4 |
        +----+-----------+---------+


        We would then have a Foreign Key constraint, such that the database will enforce that the PersonId and TaskIds have to be valid IDs for those foreign items. For the first row, we can see PersonId is 1, so Alfred, is assigned to TaskId 3, Milking cows.



        What you should be able to see here is that you could have as few or as many assignments per task or per person as you want. In this example, Ezekiel isn't assigned any tasks, and Alfred is assigned 2. If you have one task with 100 people, doing SELECT PersonId from Assignments WHERE TaskId=<whatever>; will yield 100 rows, with a variety of different Persons assigned. You can WHERE on the PersonId to find all of the tasks assigned to that person.



        If you want to return queries replacing the Ids with the Names and the tasks, then you get to learn how to JOIN tables.






        share













        share


        share








        edited 2 days ago

























        answered 2 days ago









        whatsisname

        23.6k136382




        23.6k136382








        • 45




          @linus72982: your assumption is correct, this is indeed a standard technique in database design for modelling N:M relationships. Unfortunately, it does not have a standard name, it's called "association table", "junction table", "join table", and probably a few other names as well.
          – Michael Borgwardt
          2 days ago






        • 59




          The keyword you want to search to learn more is "many-to-many relationship"
          – BlueRaja - Danny Pflughoeft
          2 days ago








        • 22




          To elaborate a little on Thierrys comment: You may think that you do not need to normalize because I only need X and it is very simple to store the ID list, but for any system that may get extended later you will regret not having normalized it earlier. Always normalize; the only question is to what normal form
          – Jan Doggen
          2 days ago








        • 5




          @Deduplicator: it's just a representation of a garden-variety, auto-increment integer primary key column. Pretty typical stuff.
          – whatsisname
          yesterday








        • 16




          I see what you did there.
          – Mac
          yesterday














        • 45




          @linus72982: your assumption is correct, this is indeed a standard technique in database design for modelling N:M relationships. Unfortunately, it does not have a standard name, it's called "association table", "junction table", "join table", and probably a few other names as well.
          – Michael Borgwardt
          2 days ago






        • 59




          The keyword you want to search to learn more is "many-to-many relationship"
          – BlueRaja - Danny Pflughoeft
          2 days ago








        • 22




          To elaborate a little on Thierrys comment: You may think that you do not need to normalize because I only need X and it is very simple to store the ID list, but for any system that may get extended later you will regret not having normalized it earlier. Always normalize; the only question is to what normal form
          – Jan Doggen
          2 days ago








        • 5




          @Deduplicator: it's just a representation of a garden-variety, auto-increment integer primary key column. Pretty typical stuff.
          – whatsisname
          yesterday








        • 16




          I see what you did there.
          – Mac
          yesterday








        45




        45




        @linus72982: your assumption is correct, this is indeed a standard technique in database design for modelling N:M relationships. Unfortunately, it does not have a standard name, it's called "association table", "junction table", "join table", and probably a few other names as well.
        – Michael Borgwardt
        2 days ago




        @linus72982: your assumption is correct, this is indeed a standard technique in database design for modelling N:M relationships. Unfortunately, it does not have a standard name, it's called "association table", "junction table", "join table", and probably a few other names as well.
        – Michael Borgwardt
        2 days ago




        59




        59




        The keyword you want to search to learn more is "many-to-many relationship"
        – BlueRaja - Danny Pflughoeft
        2 days ago






        The keyword you want to search to learn more is "many-to-many relationship"
        – BlueRaja - Danny Pflughoeft
        2 days ago






        22




        22




        To elaborate a little on Thierrys comment: You may think that you do not need to normalize because I only need X and it is very simple to store the ID list, but for any system that may get extended later you will regret not having normalized it earlier. Always normalize; the only question is to what normal form
        – Jan Doggen
        2 days ago






        To elaborate a little on Thierrys comment: You may think that you do not need to normalize because I only need X and it is very simple to store the ID list, but for any system that may get extended later you will regret not having normalized it earlier. Always normalize; the only question is to what normal form
        – Jan Doggen
        2 days ago






        5




        5




        @Deduplicator: it's just a representation of a garden-variety, auto-increment integer primary key column. Pretty typical stuff.
        – whatsisname
        yesterday






        @Deduplicator: it's just a representation of a garden-variety, auto-increment integer primary key column. Pretty typical stuff.
        – whatsisname
        yesterday






        16




        16




        I see what you did there.
        – Mac
        yesterday




        I see what you did there.
        – Mac
        yesterday












        up vote
        25
        down vote













        You're asking two questions here.



        First, you ask if its ok to store lists serialized in a column. Yes, its fine. If your project calls for it. An example might be product ingredients for a catalog page, where you have no desire to try to track each ingredient individually.



        Unfortunately your second question describes a scenario where you should opt for a more relational approach. You'll need 3 tables. One for the people, one for the tasks, and one that maintains the list of which task is assigned to which people. That last one would be vertical, one row per person/task combination, with columns for your primary key, task id, and person id.






        share|improve this answer

















        • 8




          The ingredient example you reference is correct on the surface; but it would be plaintext in that case. It is not a list in the programming sense (unless you mean that the string is a list of characters which you obviously don't). OP describing their data as "a list of IDs" (or even just "a list of [..]") implies that they are at some point handling this data as individual objects.
          – Flater
          2 days ago








        • 6




          @Flater: But it is a list. You need to be able to reformat it as (variously) an HTML list, a Markdown list, a JSON list, etc. in order to ensure the items are displayed properly in (variously) a web page, a plain text document, a mobile app... and you can't really do that with plain text.
          – Kevin
          yesterday








        • 7




          @Kevin If that is your goal, then it is much more readily and easily achieved by storing the ingredients in a table! Not to mention if, later, people would ... oh, I don't know, say, wish for recommended substitutes, or something silly like look for all recipes without any peanuts, or gluten, or animal proteins...
          – Dan Bron
          yesterday








        • 7




          @DanBron: YAGNI. Right now we're only using a list because it makes the UI logic easier. If we need or will need list-like behavior in the business logic layer, then it should be normalized into a separate table. Tables and joins are not necessarily expensive, but they're not free, and they bring in questions about element order ("Do we care about the order of ingredients?") and further normalization ("Are you going to turn '3 eggs' into ('eggs', 3)? What about 'Salt, to taste', is that ('salt', NULL)?").
          – Kevin
          yesterday








        • 3




          @Kevin: YAGNI is quite wrong here. You yourself argued the necessity of being able to transform the list in many ways (HTML, markdown, JSON) and thus are arguing that you need the individual elements of the list. Unless the data storage and "list handling" applications are two applications that are developed independently (and do note that separate application layers != separate applications), the database structure should always be created to store the data in a format that leaves it readily available - while avoiding additional parsing/conversion logic.
          – Flater
          yesterday

















        up vote
        25
        down vote













        You're asking two questions here.



        First, you ask if its ok to store lists serialized in a column. Yes, its fine. If your project calls for it. An example might be product ingredients for a catalog page, where you have no desire to try to track each ingredient individually.



        Unfortunately your second question describes a scenario where you should opt for a more relational approach. You'll need 3 tables. One for the people, one for the tasks, and one that maintains the list of which task is assigned to which people. That last one would be vertical, one row per person/task combination, with columns for your primary key, task id, and person id.






        share|improve this answer

















        • 8




          The ingredient example you reference is correct on the surface; but it would be plaintext in that case. It is not a list in the programming sense (unless you mean that the string is a list of characters which you obviously don't). OP describing their data as "a list of IDs" (or even just "a list of [..]") implies that they are at some point handling this data as individual objects.
          – Flater
          2 days ago








        • 6




          @Flater: But it is a list. You need to be able to reformat it as (variously) an HTML list, a Markdown list, a JSON list, etc. in order to ensure the items are displayed properly in (variously) a web page, a plain text document, a mobile app... and you can't really do that with plain text.
          – Kevin
          yesterday








        • 7




          @Kevin If that is your goal, then it is much more readily and easily achieved by storing the ingredients in a table! Not to mention if, later, people would ... oh, I don't know, say, wish for recommended substitutes, or something silly like look for all recipes without any peanuts, or gluten, or animal proteins...
          – Dan Bron
          yesterday








        • 7




          @DanBron: YAGNI. Right now we're only using a list because it makes the UI logic easier. If we need or will need list-like behavior in the business logic layer, then it should be normalized into a separate table. Tables and joins are not necessarily expensive, but they're not free, and they bring in questions about element order ("Do we care about the order of ingredients?") and further normalization ("Are you going to turn '3 eggs' into ('eggs', 3)? What about 'Salt, to taste', is that ('salt', NULL)?").
          – Kevin
          yesterday








        • 3




          @Kevin: YAGNI is quite wrong here. You yourself argued the necessity of being able to transform the list in many ways (HTML, markdown, JSON) and thus are arguing that you need the individual elements of the list. Unless the data storage and "list handling" applications are two applications that are developed independently (and do note that separate application layers != separate applications), the database structure should always be created to store the data in a format that leaves it readily available - while avoiding additional parsing/conversion logic.
          – Flater
          yesterday















        up vote
        25
        down vote










        up vote
        25
        down vote









        You're asking two questions here.



        First, you ask if its ok to store lists serialized in a column. Yes, its fine. If your project calls for it. An example might be product ingredients for a catalog page, where you have no desire to try to track each ingredient individually.



        Unfortunately your second question describes a scenario where you should opt for a more relational approach. You'll need 3 tables. One for the people, one for the tasks, and one that maintains the list of which task is assigned to which people. That last one would be vertical, one row per person/task combination, with columns for your primary key, task id, and person id.






        share|improve this answer












        You're asking two questions here.



        First, you ask if its ok to store lists serialized in a column. Yes, its fine. If your project calls for it. An example might be product ingredients for a catalog page, where you have no desire to try to track each ingredient individually.



        Unfortunately your second question describes a scenario where you should opt for a more relational approach. You'll need 3 tables. One for the people, one for the tasks, and one that maintains the list of which task is assigned to which people. That last one would be vertical, one row per person/task combination, with columns for your primary key, task id, and person id.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 2 days ago









        GrandmasterB

        34.9k569121




        34.9k569121








        • 8




          The ingredient example you reference is correct on the surface; but it would be plaintext in that case. It is not a list in the programming sense (unless you mean that the string is a list of characters which you obviously don't). OP describing their data as "a list of IDs" (or even just "a list of [..]") implies that they are at some point handling this data as individual objects.
          – Flater
          2 days ago








        • 6




          @Flater: But it is a list. You need to be able to reformat it as (variously) an HTML list, a Markdown list, a JSON list, etc. in order to ensure the items are displayed properly in (variously) a web page, a plain text document, a mobile app... and you can't really do that with plain text.
          – Kevin
          yesterday








        • 7




          @Kevin If that is your goal, then it is much more readily and easily achieved by storing the ingredients in a table! Not to mention if, later, people would ... oh, I don't know, say, wish for recommended substitutes, or something silly like look for all recipes without any peanuts, or gluten, or animal proteins...
          – Dan Bron
          yesterday








        • 7




          @DanBron: YAGNI. Right now we're only using a list because it makes the UI logic easier. If we need or will need list-like behavior in the business logic layer, then it should be normalized into a separate table. Tables and joins are not necessarily expensive, but they're not free, and they bring in questions about element order ("Do we care about the order of ingredients?") and further normalization ("Are you going to turn '3 eggs' into ('eggs', 3)? What about 'Salt, to taste', is that ('salt', NULL)?").
          – Kevin
          yesterday








        • 3




          @Kevin: YAGNI is quite wrong here. You yourself argued the necessity of being able to transform the list in many ways (HTML, markdown, JSON) and thus are arguing that you need the individual elements of the list. Unless the data storage and "list handling" applications are two applications that are developed independently (and do note that separate application layers != separate applications), the database structure should always be created to store the data in a format that leaves it readily available - while avoiding additional parsing/conversion logic.
          – Flater
          yesterday
















        • 8




          The ingredient example you reference is correct on the surface; but it would be plaintext in that case. It is not a list in the programming sense (unless you mean that the string is a list of characters which you obviously don't). OP describing their data as "a list of IDs" (or even just "a list of [..]") implies that they are at some point handling this data as individual objects.
          – Flater
          2 days ago








        • 6




          @Flater: But it is a list. You need to be able to reformat it as (variously) an HTML list, a Markdown list, a JSON list, etc. in order to ensure the items are displayed properly in (variously) a web page, a plain text document, a mobile app... and you can't really do that with plain text.
          – Kevin
          yesterday








        • 7




          @Kevin If that is your goal, then it is much more readily and easily achieved by storing the ingredients in a table! Not to mention if, later, people would ... oh, I don't know, say, wish for recommended substitutes, or something silly like look for all recipes without any peanuts, or gluten, or animal proteins...
          – Dan Bron
          yesterday








        • 7




          @DanBron: YAGNI. Right now we're only using a list because it makes the UI logic easier. If we need or will need list-like behavior in the business logic layer, then it should be normalized into a separate table. Tables and joins are not necessarily expensive, but they're not free, and they bring in questions about element order ("Do we care about the order of ingredients?") and further normalization ("Are you going to turn '3 eggs' into ('eggs', 3)? What about 'Salt, to taste', is that ('salt', NULL)?").
          – Kevin
          yesterday








        • 3




          @Kevin: YAGNI is quite wrong here. You yourself argued the necessity of being able to transform the list in many ways (HTML, markdown, JSON) and thus are arguing that you need the individual elements of the list. Unless the data storage and "list handling" applications are two applications that are developed independently (and do note that separate application layers != separate applications), the database structure should always be created to store the data in a format that leaves it readily available - while avoiding additional parsing/conversion logic.
          – Flater
          yesterday










        8




        8




        The ingredient example you reference is correct on the surface; but it would be plaintext in that case. It is not a list in the programming sense (unless you mean that the string is a list of characters which you obviously don't). OP describing their data as "a list of IDs" (or even just "a list of [..]") implies that they are at some point handling this data as individual objects.
        – Flater
        2 days ago






        The ingredient example you reference is correct on the surface; but it would be plaintext in that case. It is not a list in the programming sense (unless you mean that the string is a list of characters which you obviously don't). OP describing their data as "a list of IDs" (or even just "a list of [..]") implies that they are at some point handling this data as individual objects.
        – Flater
        2 days ago






        6




        6




        @Flater: But it is a list. You need to be able to reformat it as (variously) an HTML list, a Markdown list, a JSON list, etc. in order to ensure the items are displayed properly in (variously) a web page, a plain text document, a mobile app... and you can't really do that with plain text.
        – Kevin
        yesterday






        @Flater: But it is a list. You need to be able to reformat it as (variously) an HTML list, a Markdown list, a JSON list, etc. in order to ensure the items are displayed properly in (variously) a web page, a plain text document, a mobile app... and you can't really do that with plain text.
        – Kevin
        yesterday






        7




        7




        @Kevin If that is your goal, then it is much more readily and easily achieved by storing the ingredients in a table! Not to mention if, later, people would ... oh, I don't know, say, wish for recommended substitutes, or something silly like look for all recipes without any peanuts, or gluten, or animal proteins...
        – Dan Bron
        yesterday






        @Kevin If that is your goal, then it is much more readily and easily achieved by storing the ingredients in a table! Not to mention if, later, people would ... oh, I don't know, say, wish for recommended substitutes, or something silly like look for all recipes without any peanuts, or gluten, or animal proteins...
        – Dan Bron
        yesterday






        7




        7




        @DanBron: YAGNI. Right now we're only using a list because it makes the UI logic easier. If we need or will need list-like behavior in the business logic layer, then it should be normalized into a separate table. Tables and joins are not necessarily expensive, but they're not free, and they bring in questions about element order ("Do we care about the order of ingredients?") and further normalization ("Are you going to turn '3 eggs' into ('eggs', 3)? What about 'Salt, to taste', is that ('salt', NULL)?").
        – Kevin
        yesterday






        @DanBron: YAGNI. Right now we're only using a list because it makes the UI logic easier. If we need or will need list-like behavior in the business logic layer, then it should be normalized into a separate table. Tables and joins are not necessarily expensive, but they're not free, and they bring in questions about element order ("Do we care about the order of ingredients?") and further normalization ("Are you going to turn '3 eggs' into ('eggs', 3)? What about 'Salt, to taste', is that ('salt', NULL)?").
        – Kevin
        yesterday






        3




        3




        @Kevin: YAGNI is quite wrong here. You yourself argued the necessity of being able to transform the list in many ways (HTML, markdown, JSON) and thus are arguing that you need the individual elements of the list. Unless the data storage and "list handling" applications are two applications that are developed independently (and do note that separate application layers != separate applications), the database structure should always be created to store the data in a format that leaves it readily available - while avoiding additional parsing/conversion logic.
        – Flater
        yesterday






        @Kevin: YAGNI is quite wrong here. You yourself argued the necessity of being able to transform the list in many ways (HTML, markdown, JSON) and thus are arguing that you need the individual elements of the list. Unless the data storage and "list handling" applications are two applications that are developed independently (and do note that separate application layers != separate applications), the database structure should always be created to store the data in a format that leaves it readily available - while avoiding additional parsing/conversion logic.
        – Flater
        yesterday












        up vote
        14
        down vote













        What you're describing is known as a "many to many" relationship, in your case between Person and Task. It's typically implemented using a third table, sometimes called a "link" or "cross-reference" table. For example:



        create table person (
        person_id integer primary key,
        ...
        );

        create table task (
        task_id integer primary key,
        ...
        );

        create table person_task_xref (
        person_id integer not null,
        task_id integer not null,
        primary key (person_id, task_id),
        foreign key (person_id) references person (person_id),
        foreign key (task_id) references task (task_id)
        );





        share|improve this answer

























          up vote
          14
          down vote













          What you're describing is known as a "many to many" relationship, in your case between Person and Task. It's typically implemented using a third table, sometimes called a "link" or "cross-reference" table. For example:



          create table person (
          person_id integer primary key,
          ...
          );

          create table task (
          task_id integer primary key,
          ...
          );

          create table person_task_xref (
          person_id integer not null,
          task_id integer not null,
          primary key (person_id, task_id),
          foreign key (person_id) references person (person_id),
          foreign key (task_id) references task (task_id)
          );





          share|improve this answer























            up vote
            14
            down vote










            up vote
            14
            down vote









            What you're describing is known as a "many to many" relationship, in your case between Person and Task. It's typically implemented using a third table, sometimes called a "link" or "cross-reference" table. For example:



            create table person (
            person_id integer primary key,
            ...
            );

            create table task (
            task_id integer primary key,
            ...
            );

            create table person_task_xref (
            person_id integer not null,
            task_id integer not null,
            primary key (person_id, task_id),
            foreign key (person_id) references person (person_id),
            foreign key (task_id) references task (task_id)
            );





            share|improve this answer












            What you're describing is known as a "many to many" relationship, in your case between Person and Task. It's typically implemented using a third table, sometimes called a "link" or "cross-reference" table. For example:



            create table person (
            person_id integer primary key,
            ...
            );

            create table task (
            task_id integer primary key,
            ...
            );

            create table person_task_xref (
            person_id integer not null,
            task_id integer not null,
            primary key (person_id, task_id),
            foreign key (person_id) references person (person_id),
            foreign key (task_id) references task (task_id)
            );






            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered 2 days ago









            Mike Partridge

            5,24711738




            5,24711738






















                up vote
                9
                down vote














                ... it's never (or almost never) okay to store a list of IDs or the like in a field




                The only time you might store more than one data item in a single field is when that field is only ever used as a single entity and is never considered as being made up of those smaller elements. An example might be an image, stored in a BLOB field. It's made up of lots and lots of smaller elements (bytes) but these that mean nothing to the database and can only be used all together (and look pretty to an End User).



                Since a "list" is, by definition, made up of smaller elements (items), this isn't the case here and you should normalise the data.




                ... if I save these tasks individually in "Person", I'll have to have dozens of dummy "TaskID" columns ...




                No. You'll have a few rows in an Intersection Table (a.k.a. Weak Entity) between Person and Task. Databases are really good at working with lots of rows; they're actually pretty rubbish at working with lots of [repeated] columns.



                Nice clear example given by whatsisname.






                share|improve this answer

















                • 1




                  When creating real life systems "never say never" is a very good rule to live by.
                  – l0b0
                  yesterday















                up vote
                9
                down vote














                ... it's never (or almost never) okay to store a list of IDs or the like in a field




                The only time you might store more than one data item in a single field is when that field is only ever used as a single entity and is never considered as being made up of those smaller elements. An example might be an image, stored in a BLOB field. It's made up of lots and lots of smaller elements (bytes) but these that mean nothing to the database and can only be used all together (and look pretty to an End User).



                Since a "list" is, by definition, made up of smaller elements (items), this isn't the case here and you should normalise the data.




                ... if I save these tasks individually in "Person", I'll have to have dozens of dummy "TaskID" columns ...




                No. You'll have a few rows in an Intersection Table (a.k.a. Weak Entity) between Person and Task. Databases are really good at working with lots of rows; they're actually pretty rubbish at working with lots of [repeated] columns.



                Nice clear example given by whatsisname.






                share|improve this answer

















                • 1




                  When creating real life systems "never say never" is a very good rule to live by.
                  – l0b0
                  yesterday













                up vote
                9
                down vote










                up vote
                9
                down vote










                ... it's never (or almost never) okay to store a list of IDs or the like in a field




                The only time you might store more than one data item in a single field is when that field is only ever used as a single entity and is never considered as being made up of those smaller elements. An example might be an image, stored in a BLOB field. It's made up of lots and lots of smaller elements (bytes) but these that mean nothing to the database and can only be used all together (and look pretty to an End User).



                Since a "list" is, by definition, made up of smaller elements (items), this isn't the case here and you should normalise the data.




                ... if I save these tasks individually in "Person", I'll have to have dozens of dummy "TaskID" columns ...




                No. You'll have a few rows in an Intersection Table (a.k.a. Weak Entity) between Person and Task. Databases are really good at working with lots of rows; they're actually pretty rubbish at working with lots of [repeated] columns.



                Nice clear example given by whatsisname.






                share|improve this answer













                ... it's never (or almost never) okay to store a list of IDs or the like in a field




                The only time you might store more than one data item in a single field is when that field is only ever used as a single entity and is never considered as being made up of those smaller elements. An example might be an image, stored in a BLOB field. It's made up of lots and lots of smaller elements (bytes) but these that mean nothing to the database and can only be used all together (and look pretty to an End User).



                Since a "list" is, by definition, made up of smaller elements (items), this isn't the case here and you should normalise the data.




                ... if I save these tasks individually in "Person", I'll have to have dozens of dummy "TaskID" columns ...




                No. You'll have a few rows in an Intersection Table (a.k.a. Weak Entity) between Person and Task. Databases are really good at working with lots of rows; they're actually pretty rubbish at working with lots of [repeated] columns.



                Nice clear example given by whatsisname.







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered 2 days ago









                Phill W.

                7,6883726




                7,6883726








                • 1




                  When creating real life systems "never say never" is a very good rule to live by.
                  – l0b0
                  yesterday














                • 1




                  When creating real life systems "never say never" is a very good rule to live by.
                  – l0b0
                  yesterday








                1




                1




                When creating real life systems "never say never" is a very good rule to live by.
                – l0b0
                yesterday




                When creating real life systems "never say never" is a very good rule to live by.
                – l0b0
                yesterday










                up vote
                2
                down vote













                It may be legitimate in certain pre-calculated fields.



                If some of your queries are expensive and you decide to go with pre-calculated fields updated automatically using database triggers, then it may be legitimate to keep the lists inside a column.



                For example, in the UI you want to show this list using grid view, where each row can open full details (with complete lists) after double-clicking:



                REGISTERED USER LIST
                +------------------+----------------------------------------------------+
                |Name |Top 3 most visited tags |
                +==================+====================================================+
                |Peter |Design, Fitness, Gifts |
                +------------------+----------------------------------------------------+
                |Lucy |Fashion, Gifts, Lifestyle |
                +------------------+----------------------------------------------------+


                You are keeping the second column updated by trigger when client visits new article or by scheduled task.



                You can make such a field available even for searching (as normal text).



                For such cases, keeping lists is legitimate. You just need to consider case of possibly exceeding maximum field length.





                Also, if you are using Microsoft Access, offered multivalued fields are another special use case. They handle your lists in a field automatically.



                But you can always fall back to standard normalized form shown in other answers.





                Summary: Normal forms of database are theoretical model required for understanding important aspects of data modeling. But of course normalization does not take into account performance or other cost of retrieving the data. It is out of scope of that theoretical model. But storing lists or other pre-calculated (and controlled) duplicates is often required by practical implementation.



                In the light of the above, in practical implementation, would we prefer query relying on perfect normal form and running 20 seconds or equivalent query relying on pre-calculated values which takes 0.08 s? No one likes their software product to be accused of slowness.






                share|improve this answer



















                • 1




                  It can be legitimate even without precalculated stuff. I've done it a couple of times where the data is stored properly but for performance reasons it's useful to stuff a few cached results in the main records.
                  – Loren Pechtel
                  yesterday










                • @LorenPechtel – Yes, thanks, in my use of term pre-calculated I also include cases of cached values stored where needed. In systems with complex dependencies, they are the way to keep the performance normal. And if programmed with adequate know-how, these values are reliable and always-in-sync. I just did not want to add case of caching into the answer to keep the answer simple and on safe side. It got downvoted anyway. :)
                  – miroxlav
                  yesterday

















                up vote
                2
                down vote













                It may be legitimate in certain pre-calculated fields.



                If some of your queries are expensive and you decide to go with pre-calculated fields updated automatically using database triggers, then it may be legitimate to keep the lists inside a column.



                For example, in the UI you want to show this list using grid view, where each row can open full details (with complete lists) after double-clicking:



                REGISTERED USER LIST
                +------------------+----------------------------------------------------+
                |Name |Top 3 most visited tags |
                +==================+====================================================+
                |Peter |Design, Fitness, Gifts |
                +------------------+----------------------------------------------------+
                |Lucy |Fashion, Gifts, Lifestyle |
                +------------------+----------------------------------------------------+


                You are keeping the second column updated by trigger when client visits new article or by scheduled task.



                You can make such a field available even for searching (as normal text).



                For such cases, keeping lists is legitimate. You just need to consider case of possibly exceeding maximum field length.





                Also, if you are using Microsoft Access, offered multivalued fields are another special use case. They handle your lists in a field automatically.



                But you can always fall back to standard normalized form shown in other answers.





                Summary: Normal forms of database are theoretical model required for understanding important aspects of data modeling. But of course normalization does not take into account performance or other cost of retrieving the data. It is out of scope of that theoretical model. But storing lists or other pre-calculated (and controlled) duplicates is often required by practical implementation.



                In the light of the above, in practical implementation, would we prefer query relying on perfect normal form and running 20 seconds or equivalent query relying on pre-calculated values which takes 0.08 s? No one likes their software product to be accused of slowness.






                share|improve this answer



















                • 1




                  It can be legitimate even without precalculated stuff. I've done it a couple of times where the data is stored properly but for performance reasons it's useful to stuff a few cached results in the main records.
                  – Loren Pechtel
                  yesterday










                • @LorenPechtel – Yes, thanks, in my use of term pre-calculated I also include cases of cached values stored where needed. In systems with complex dependencies, they are the way to keep the performance normal. And if programmed with adequate know-how, these values are reliable and always-in-sync. I just did not want to add case of caching into the answer to keep the answer simple and on safe side. It got downvoted anyway. :)
                  – miroxlav
                  yesterday















                up vote
                2
                down vote










                up vote
                2
                down vote









                It may be legitimate in certain pre-calculated fields.



                If some of your queries are expensive and you decide to go with pre-calculated fields updated automatically using database triggers, then it may be legitimate to keep the lists inside a column.



                For example, in the UI you want to show this list using grid view, where each row can open full details (with complete lists) after double-clicking:



                REGISTERED USER LIST
                +------------------+----------------------------------------------------+
                |Name |Top 3 most visited tags |
                +==================+====================================================+
                |Peter |Design, Fitness, Gifts |
                +------------------+----------------------------------------------------+
                |Lucy |Fashion, Gifts, Lifestyle |
                +------------------+----------------------------------------------------+


                You are keeping the second column updated by trigger when client visits new article or by scheduled task.



                You can make such a field available even for searching (as normal text).



                For such cases, keeping lists is legitimate. You just need to consider case of possibly exceeding maximum field length.





                Also, if you are using Microsoft Access, offered multivalued fields are another special use case. They handle your lists in a field automatically.



                But you can always fall back to standard normalized form shown in other answers.





                Summary: Normal forms of database are theoretical model required for understanding important aspects of data modeling. But of course normalization does not take into account performance or other cost of retrieving the data. It is out of scope of that theoretical model. But storing lists or other pre-calculated (and controlled) duplicates is often required by practical implementation.



                In the light of the above, in practical implementation, would we prefer query relying on perfect normal form and running 20 seconds or equivalent query relying on pre-calculated values which takes 0.08 s? No one likes their software product to be accused of slowness.






                share|improve this answer














                It may be legitimate in certain pre-calculated fields.



                If some of your queries are expensive and you decide to go with pre-calculated fields updated automatically using database triggers, then it may be legitimate to keep the lists inside a column.



                For example, in the UI you want to show this list using grid view, where each row can open full details (with complete lists) after double-clicking:



                REGISTERED USER LIST
                +------------------+----------------------------------------------------+
                |Name |Top 3 most visited tags |
                +==================+====================================================+
                |Peter |Design, Fitness, Gifts |
                +------------------+----------------------------------------------------+
                |Lucy |Fashion, Gifts, Lifestyle |
                +------------------+----------------------------------------------------+


                You are keeping the second column updated by trigger when client visits new article or by scheduled task.



                You can make such a field available even for searching (as normal text).



                For such cases, keeping lists is legitimate. You just need to consider case of possibly exceeding maximum field length.





                Also, if you are using Microsoft Access, offered multivalued fields are another special use case. They handle your lists in a field automatically.



                But you can always fall back to standard normalized form shown in other answers.





                Summary: Normal forms of database are theoretical model required for understanding important aspects of data modeling. But of course normalization does not take into account performance or other cost of retrieving the data. It is out of scope of that theoretical model. But storing lists or other pre-calculated (and controlled) duplicates is often required by practical implementation.



                In the light of the above, in practical implementation, would we prefer query relying on perfect normal form and running 20 seconds or equivalent query relying on pre-calculated values which takes 0.08 s? No one likes their software product to be accused of slowness.







                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited yesterday

























                answered yesterday









                miroxlav

                444211




                444211








                • 1




                  It can be legitimate even without precalculated stuff. I've done it a couple of times where the data is stored properly but for performance reasons it's useful to stuff a few cached results in the main records.
                  – Loren Pechtel
                  yesterday










                • @LorenPechtel – Yes, thanks, in my use of term pre-calculated I also include cases of cached values stored where needed. In systems with complex dependencies, they are the way to keep the performance normal. And if programmed with adequate know-how, these values are reliable and always-in-sync. I just did not want to add case of caching into the answer to keep the answer simple and on safe side. It got downvoted anyway. :)
                  – miroxlav
                  yesterday
















                • 1




                  It can be legitimate even without precalculated stuff. I've done it a couple of times where the data is stored properly but for performance reasons it's useful to stuff a few cached results in the main records.
                  – Loren Pechtel
                  yesterday










                • @LorenPechtel – Yes, thanks, in my use of term pre-calculated I also include cases of cached values stored where needed. In systems with complex dependencies, they are the way to keep the performance normal. And if programmed with adequate know-how, these values are reliable and always-in-sync. I just did not want to add case of caching into the answer to keep the answer simple and on safe side. It got downvoted anyway. :)
                  – miroxlav
                  yesterday










                1




                1




                It can be legitimate even without precalculated stuff. I've done it a couple of times where the data is stored properly but for performance reasons it's useful to stuff a few cached results in the main records.
                – Loren Pechtel
                yesterday




                It can be legitimate even without precalculated stuff. I've done it a couple of times where the data is stored properly but for performance reasons it's useful to stuff a few cached results in the main records.
                – Loren Pechtel
                yesterday












                @LorenPechtel – Yes, thanks, in my use of term pre-calculated I also include cases of cached values stored where needed. In systems with complex dependencies, they are the way to keep the performance normal. And if programmed with adequate know-how, these values are reliable and always-in-sync. I just did not want to add case of caching into the answer to keep the answer simple and on safe side. It got downvoted anyway. :)
                – miroxlav
                yesterday






                @LorenPechtel – Yes, thanks, in my use of term pre-calculated I also include cases of cached values stored where needed. In systems with complex dependencies, they are the way to keep the performance normal. And if programmed with adequate know-how, these values are reliable and always-in-sync. I just did not want to add case of caching into the answer to keep the answer simple and on safe side. It got downvoted anyway. :)
                – miroxlav
                yesterday












                up vote
                0
                down vote













                Given two tables; we'll call them Person and Task, each with it's own ID (PersonID, TaskID)... the basic idea is to create a third table to bind them together. We'll call this table PersonToTask. At the minimum it should have it's own ID, as well as the two others
                So when it comes to assigning someone to a task; you will no longer need to UPDATE the Person table, you just need to INSERT a new line into the PersonToTaskTable.
                And maintenance becomes easier- need to delete a task just becomes a DELETE based on TaskID, no more updating the Person table and it's associated parsing



                CREATE TABLE dbo.PersonToTask (
                pttID INT IDENTITY(1,1) NOT NULL,
                PersonID INT NULL,
                TaskID INT NULL
                )

                CREATE PROCEDURE dbo.Task_Assigned (@PersonID INT, @TaskID INT)
                AS
                BEGIN
                INSERT PersonToTask (PersonID, TaskID)
                VALUES (@PersonID, @TaskID)
                END

                CREATE PROCEDURE dbo.Task_Deleted (@TaskID INT)
                AS
                BEGIN
                DELETE PersonToTask WHERE TaskID = @TaskID
                DELETE Task WHERE TaskID = @TaskID
                END


                How about a simple report or who's all assigned to a task?



                CREATE PROCEDURE dbo.Task_CurrentAssigned (@TaskID INT)
                AS
                BEGIN
                SELECT PersonName
                FROM dbo.Person
                WHERE PersonID IN (SELECT PersonID FROM dbo.PersonToTask WHERE TaskID = @TaskID)
                END


                You of course could do a lot more; a TimeReport could be done if you added DateTime fields for TaskAssigned and TaskCompleted. It's all up to you






                share|improve this answer








                New contributor




                Mad Myche is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                Check out our Code of Conduct.






















                  up vote
                  0
                  down vote













                  Given two tables; we'll call them Person and Task, each with it's own ID (PersonID, TaskID)... the basic idea is to create a third table to bind them together. We'll call this table PersonToTask. At the minimum it should have it's own ID, as well as the two others
                  So when it comes to assigning someone to a task; you will no longer need to UPDATE the Person table, you just need to INSERT a new line into the PersonToTaskTable.
                  And maintenance becomes easier- need to delete a task just becomes a DELETE based on TaskID, no more updating the Person table and it's associated parsing



                  CREATE TABLE dbo.PersonToTask (
                  pttID INT IDENTITY(1,1) NOT NULL,
                  PersonID INT NULL,
                  TaskID INT NULL
                  )

                  CREATE PROCEDURE dbo.Task_Assigned (@PersonID INT, @TaskID INT)
                  AS
                  BEGIN
                  INSERT PersonToTask (PersonID, TaskID)
                  VALUES (@PersonID, @TaskID)
                  END

                  CREATE PROCEDURE dbo.Task_Deleted (@TaskID INT)
                  AS
                  BEGIN
                  DELETE PersonToTask WHERE TaskID = @TaskID
                  DELETE Task WHERE TaskID = @TaskID
                  END


                  How about a simple report or who's all assigned to a task?



                  CREATE PROCEDURE dbo.Task_CurrentAssigned (@TaskID INT)
                  AS
                  BEGIN
                  SELECT PersonName
                  FROM dbo.Person
                  WHERE PersonID IN (SELECT PersonID FROM dbo.PersonToTask WHERE TaskID = @TaskID)
                  END


                  You of course could do a lot more; a TimeReport could be done if you added DateTime fields for TaskAssigned and TaskCompleted. It's all up to you






                  share|improve this answer








                  New contributor




                  Mad Myche is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                  Check out our Code of Conduct.




















                    up vote
                    0
                    down vote










                    up vote
                    0
                    down vote









                    Given two tables; we'll call them Person and Task, each with it's own ID (PersonID, TaskID)... the basic idea is to create a third table to bind them together. We'll call this table PersonToTask. At the minimum it should have it's own ID, as well as the two others
                    So when it comes to assigning someone to a task; you will no longer need to UPDATE the Person table, you just need to INSERT a new line into the PersonToTaskTable.
                    And maintenance becomes easier- need to delete a task just becomes a DELETE based on TaskID, no more updating the Person table and it's associated parsing



                    CREATE TABLE dbo.PersonToTask (
                    pttID INT IDENTITY(1,1) NOT NULL,
                    PersonID INT NULL,
                    TaskID INT NULL
                    )

                    CREATE PROCEDURE dbo.Task_Assigned (@PersonID INT, @TaskID INT)
                    AS
                    BEGIN
                    INSERT PersonToTask (PersonID, TaskID)
                    VALUES (@PersonID, @TaskID)
                    END

                    CREATE PROCEDURE dbo.Task_Deleted (@TaskID INT)
                    AS
                    BEGIN
                    DELETE PersonToTask WHERE TaskID = @TaskID
                    DELETE Task WHERE TaskID = @TaskID
                    END


                    How about a simple report or who's all assigned to a task?



                    CREATE PROCEDURE dbo.Task_CurrentAssigned (@TaskID INT)
                    AS
                    BEGIN
                    SELECT PersonName
                    FROM dbo.Person
                    WHERE PersonID IN (SELECT PersonID FROM dbo.PersonToTask WHERE TaskID = @TaskID)
                    END


                    You of course could do a lot more; a TimeReport could be done if you added DateTime fields for TaskAssigned and TaskCompleted. It's all up to you






                    share|improve this answer








                    New contributor




                    Mad Myche is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.









                    Given two tables; we'll call them Person and Task, each with it's own ID (PersonID, TaskID)... the basic idea is to create a third table to bind them together. We'll call this table PersonToTask. At the minimum it should have it's own ID, as well as the two others
                    So when it comes to assigning someone to a task; you will no longer need to UPDATE the Person table, you just need to INSERT a new line into the PersonToTaskTable.
                    And maintenance becomes easier- need to delete a task just becomes a DELETE based on TaskID, no more updating the Person table and it's associated parsing



                    CREATE TABLE dbo.PersonToTask (
                    pttID INT IDENTITY(1,1) NOT NULL,
                    PersonID INT NULL,
                    TaskID INT NULL
                    )

                    CREATE PROCEDURE dbo.Task_Assigned (@PersonID INT, @TaskID INT)
                    AS
                    BEGIN
                    INSERT PersonToTask (PersonID, TaskID)
                    VALUES (@PersonID, @TaskID)
                    END

                    CREATE PROCEDURE dbo.Task_Deleted (@TaskID INT)
                    AS
                    BEGIN
                    DELETE PersonToTask WHERE TaskID = @TaskID
                    DELETE Task WHERE TaskID = @TaskID
                    END


                    How about a simple report or who's all assigned to a task?



                    CREATE PROCEDURE dbo.Task_CurrentAssigned (@TaskID INT)
                    AS
                    BEGIN
                    SELECT PersonName
                    FROM dbo.Person
                    WHERE PersonID IN (SELECT PersonID FROM dbo.PersonToTask WHERE TaskID = @TaskID)
                    END


                    You of course could do a lot more; a TimeReport could be done if you added DateTime fields for TaskAssigned and TaskCompleted. It's all up to you







                    share|improve this answer








                    New contributor




                    Mad Myche is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.









                    share|improve this answer



                    share|improve this answer






                    New contributor




                    Mad Myche is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.









                    answered yesterday









                    Mad Myche

                    1012




                    1012




                    New contributor




                    Mad Myche is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.





                    New contributor





                    Mad Myche is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.






                    Mad Myche is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                    Check out our Code of Conduct.






















                        up vote
                        0
                        down vote













                        It may work if say you have human readable Primary keys and want a list of task #'s without having to deal with vertical nature of a table structure. i.e. much easier to read first table.



                        ------------------------  
                        Employee Name | Task
                        Jack | 1,2,5
                        Jill | 4,6,7
                        ------------------------

                        ------------------------
                        Employee Name | Task
                        Jack | 1
                        Jack | 2
                        Jack | 5
                        Jill | 4
                        Jill | 6
                        Jill | 7
                        ------------------------


                        The question would then be: should the task list be stored or generated on demand, which largely would depend on requirements such as: how often the list are needed, how accurate how many data rows exist, how the data will be used, etc... after which analyzing the trade offs to user experience and meeting requirements should be done.



                        For example comparing the time it would take to recall the 2 rows vs running a query that would generate the 2 rows. If it takes long and the user does not need the most up to date list(*expecting less than 1 change per day) then it could be stored.



                        Or if the user needs a historical record of tasks assigned to them it would also make sense if the list was stored. So it really depends on what you are doing, never say never.






                        share|improve this answer








                        New contributor




                        Double E CPU is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                        • As you say, it all depends on how the data is to be retrieved. If you /only/ ever query this table by User Name, then the "list" field is perfectly adequate. However, how can you query such a table to find out who is working on Task #1234567 and still keep it performant? Just about every kind of "find-X-anywhere-in-the-field" String function will cause such a query to /Table Scan/, slowing things to a crawl. With properly normalised, properly indexed data, that just doesn't happen.
                          – Phill W.
                          yesterday















                        up vote
                        0
                        down vote













                        It may work if say you have human readable Primary keys and want a list of task #'s without having to deal with vertical nature of a table structure. i.e. much easier to read first table.



                        ------------------------  
                        Employee Name | Task
                        Jack | 1,2,5
                        Jill | 4,6,7
                        ------------------------

                        ------------------------
                        Employee Name | Task
                        Jack | 1
                        Jack | 2
                        Jack | 5
                        Jill | 4
                        Jill | 6
                        Jill | 7
                        ------------------------


                        The question would then be: should the task list be stored or generated on demand, which largely would depend on requirements such as: how often the list are needed, how accurate how many data rows exist, how the data will be used, etc... after which analyzing the trade offs to user experience and meeting requirements should be done.



                        For example comparing the time it would take to recall the 2 rows vs running a query that would generate the 2 rows. If it takes long and the user does not need the most up to date list(*expecting less than 1 change per day) then it could be stored.



                        Or if the user needs a historical record of tasks assigned to them it would also make sense if the list was stored. So it really depends on what you are doing, never say never.






                        share|improve this answer








                        New contributor




                        Double E CPU is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                        Check out our Code of Conduct.


















                        • As you say, it all depends on how the data is to be retrieved. If you /only/ ever query this table by User Name, then the "list" field is perfectly adequate. However, how can you query such a table to find out who is working on Task #1234567 and still keep it performant? Just about every kind of "find-X-anywhere-in-the-field" String function will cause such a query to /Table Scan/, slowing things to a crawl. With properly normalised, properly indexed data, that just doesn't happen.
                          – Phill W.
                          yesterday













                        up vote
                        0
                        down vote










                        up vote
                        0
                        down vote









                        It may work if say you have human readable Primary keys and want a list of task #'s without having to deal with vertical nature of a table structure. i.e. much easier to read first table.



                        ------------------------  
                        Employee Name | Task
                        Jack | 1,2,5
                        Jill | 4,6,7
                        ------------------------

                        ------------------------
                        Employee Name | Task
                        Jack | 1
                        Jack | 2
                        Jack | 5
                        Jill | 4
                        Jill | 6
                        Jill | 7
                        ------------------------


                        The question would then be: should the task list be stored or generated on demand, which largely would depend on requirements such as: how often the list are needed, how accurate how many data rows exist, how the data will be used, etc... after which analyzing the trade offs to user experience and meeting requirements should be done.



                        For example comparing the time it would take to recall the 2 rows vs running a query that would generate the 2 rows. If it takes long and the user does not need the most up to date list(*expecting less than 1 change per day) then it could be stored.



                        Or if the user needs a historical record of tasks assigned to them it would also make sense if the list was stored. So it really depends on what you are doing, never say never.






                        share|improve this answer








                        New contributor




                        Double E CPU is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                        Check out our Code of Conduct.









                        It may work if say you have human readable Primary keys and want a list of task #'s without having to deal with vertical nature of a table structure. i.e. much easier to read first table.



                        ------------------------  
                        Employee Name | Task
                        Jack | 1,2,5
                        Jill | 4,6,7
                        ------------------------

                        ------------------------
                        Employee Name | Task
                        Jack | 1
                        Jack | 2
                        Jack | 5
                        Jill | 4
                        Jill | 6
                        Jill | 7
                        ------------------------


                        The question would then be: should the task list be stored or generated on demand, which largely would depend on requirements such as: how often the list are needed, how accurate how many data rows exist, how the data will be used, etc... after which analyzing the trade offs to user experience and meeting requirements should be done.



                        For example comparing the time it would take to recall the 2 rows vs running a query that would generate the 2 rows. If it takes long and the user does not need the most up to date list(*expecting less than 1 change per day) then it could be stored.



                        Or if the user needs a historical record of tasks assigned to them it would also make sense if the list was stored. So it really depends on what you are doing, never say never.







                        share|improve this answer








                        New contributor




                        Double E CPU is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                        Check out our Code of Conduct.









                        share|improve this answer



                        share|improve this answer






                        New contributor




                        Double E CPU is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                        Check out our Code of Conduct.









                        answered yesterday









                        Double E CPU

                        11




                        11




                        New contributor




                        Double E CPU is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                        Check out our Code of Conduct.





                        New contributor





                        Double E CPU is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                        Check out our Code of Conduct.






                        Double E CPU is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                        Check out our Code of Conduct.












                        • As you say, it all depends on how the data is to be retrieved. If you /only/ ever query this table by User Name, then the "list" field is perfectly adequate. However, how can you query such a table to find out who is working on Task #1234567 and still keep it performant? Just about every kind of "find-X-anywhere-in-the-field" String function will cause such a query to /Table Scan/, slowing things to a crawl. With properly normalised, properly indexed data, that just doesn't happen.
                          – Phill W.
                          yesterday


















                        • As you say, it all depends on how the data is to be retrieved. If you /only/ ever query this table by User Name, then the "list" field is perfectly adequate. However, how can you query such a table to find out who is working on Task #1234567 and still keep it performant? Just about every kind of "find-X-anywhere-in-the-field" String function will cause such a query to /Table Scan/, slowing things to a crawl. With properly normalised, properly indexed data, that just doesn't happen.
                          – Phill W.
                          yesterday
















                        As you say, it all depends on how the data is to be retrieved. If you /only/ ever query this table by User Name, then the "list" field is perfectly adequate. However, how can you query such a table to find out who is working on Task #1234567 and still keep it performant? Just about every kind of "find-X-anywhere-in-the-field" String function will cause such a query to /Table Scan/, slowing things to a crawl. With properly normalised, properly indexed data, that just doesn't happen.
                        – Phill W.
                        yesterday




                        As you say, it all depends on how the data is to be retrieved. If you /only/ ever query this table by User Name, then the "list" field is perfectly adequate. However, how can you query such a table to find out who is working on Task #1234567 and still keep it performant? Just about every kind of "find-X-anywhere-in-the-field" String function will cause such a query to /Table Scan/, slowing things to a crawl. With properly normalised, properly indexed data, that just doesn't happen.
                        – Phill W.
                        yesterday










                        up vote
                        0
                        down vote













                        You're taking what should be another table, turning it through 90 degrees and shoehorning it into another table.



                        It's like having an order table where you have itemProdcode1, itemQuantity1, itemPrice1 ... itemProdcode37, itemQuantity37, itemPrice37. Apart from being awkward to handle programmatically you can guarantee that tomorrow someone will want to order 38 things.



                        I'd only do it your way if the 'list' isn't really a list, i.e. where it stands as a whole and each individual line item doesn't refer to some clear and independent entity. In that case just stuff it all in some data type that's big enough.



                        So an order is a list, a Bill Of Materials is a list (or a list of lists, which would be even more of a nightmare to implement "sideways"). But a note/comment and a poem aren't.






                        share|improve this answer








                        New contributor




                        Bloke Down The Pub is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                          up vote
                          0
                          down vote













                          You're taking what should be another table, turning it through 90 degrees and shoehorning it into another table.



                          It's like having an order table where you have itemProdcode1, itemQuantity1, itemPrice1 ... itemProdcode37, itemQuantity37, itemPrice37. Apart from being awkward to handle programmatically you can guarantee that tomorrow someone will want to order 38 things.



                          I'd only do it your way if the 'list' isn't really a list, i.e. where it stands as a whole and each individual line item doesn't refer to some clear and independent entity. In that case just stuff it all in some data type that's big enough.



                          So an order is a list, a Bill Of Materials is a list (or a list of lists, which would be even more of a nightmare to implement "sideways"). But a note/comment and a poem aren't.






                          share|improve this answer








                          New contributor




                          Bloke Down The Pub is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                          Check out our Code of Conduct.




















                            up vote
                            0
                            down vote










                            up vote
                            0
                            down vote









                            You're taking what should be another table, turning it through 90 degrees and shoehorning it into another table.



                            It's like having an order table where you have itemProdcode1, itemQuantity1, itemPrice1 ... itemProdcode37, itemQuantity37, itemPrice37. Apart from being awkward to handle programmatically you can guarantee that tomorrow someone will want to order 38 things.



                            I'd only do it your way if the 'list' isn't really a list, i.e. where it stands as a whole and each individual line item doesn't refer to some clear and independent entity. In that case just stuff it all in some data type that's big enough.



                            So an order is a list, a Bill Of Materials is a list (or a list of lists, which would be even more of a nightmare to implement "sideways"). But a note/comment and a poem aren't.






                            share|improve this answer








                            New contributor




                            Bloke Down The Pub is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                            Check out our Code of Conduct.









                            You're taking what should be another table, turning it through 90 degrees and shoehorning it into another table.



                            It's like having an order table where you have itemProdcode1, itemQuantity1, itemPrice1 ... itemProdcode37, itemQuantity37, itemPrice37. Apart from being awkward to handle programmatically you can guarantee that tomorrow someone will want to order 38 things.



                            I'd only do it your way if the 'list' isn't really a list, i.e. where it stands as a whole and each individual line item doesn't refer to some clear and independent entity. In that case just stuff it all in some data type that's big enough.



                            So an order is a list, a Bill Of Materials is a list (or a list of lists, which would be even more of a nightmare to implement "sideways"). But a note/comment and a poem aren't.







                            share|improve this answer








                            New contributor




                            Bloke Down The Pub is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                            Check out our Code of Conduct.









                            share|improve this answer



                            share|improve this answer






                            New contributor




                            Bloke Down The Pub is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                            answered yesterday









                            Bloke Down The Pub

                            1




                            1




                            New contributor




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                            New contributor





                            Bloke Down The Pub is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                            Bloke Down The Pub is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                                protected by gnat yesterday



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