Uniqueness constraint based on column value in a related table












0














I have 2 tables, let's call it users and groups. Some groups are by design singletons and must have exactly one user, and some groups can have multiple users.



users (
id
)

groups (
id
name
singleton
)

users_groups (
user_id
group_id
)


Is there a way to enforce the uniqueness constraint that would




  • disallow adding more than one user to singleton groups

  • remove singleton groups when its only user is deleted










share|improve this question


















  • 1




    Handling both these requirements is probably best accomplished with triggers.
    – Gordon Linoff
    Nov 21 at 3:09
















0














I have 2 tables, let's call it users and groups. Some groups are by design singletons and must have exactly one user, and some groups can have multiple users.



users (
id
)

groups (
id
name
singleton
)

users_groups (
user_id
group_id
)


Is there a way to enforce the uniqueness constraint that would




  • disallow adding more than one user to singleton groups

  • remove singleton groups when its only user is deleted










share|improve this question


















  • 1




    Handling both these requirements is probably best accomplished with triggers.
    – Gordon Linoff
    Nov 21 at 3:09














0












0








0







I have 2 tables, let's call it users and groups. Some groups are by design singletons and must have exactly one user, and some groups can have multiple users.



users (
id
)

groups (
id
name
singleton
)

users_groups (
user_id
group_id
)


Is there a way to enforce the uniqueness constraint that would




  • disallow adding more than one user to singleton groups

  • remove singleton groups when its only user is deleted










share|improve this question













I have 2 tables, let's call it users and groups. Some groups are by design singletons and must have exactly one user, and some groups can have multiple users.



users (
id
)

groups (
id
name
singleton
)

users_groups (
user_id
group_id
)


Is there a way to enforce the uniqueness constraint that would




  • disallow adding more than one user to singleton groups

  • remove singleton groups when its only user is deleted







mysql sql






share|improve this question













share|improve this question











share|improve this question




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asked Nov 21 at 2:05









vasily

1,6011326




1,6011326








  • 1




    Handling both these requirements is probably best accomplished with triggers.
    – Gordon Linoff
    Nov 21 at 3:09














  • 1




    Handling both these requirements is probably best accomplished with triggers.
    – Gordon Linoff
    Nov 21 at 3:09








1




1




Handling both these requirements is probably best accomplished with triggers.
– Gordon Linoff
Nov 21 at 3:09




Handling both these requirements is probably best accomplished with triggers.
– Gordon Linoff
Nov 21 at 3:09












1 Answer
1






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Using triggers we can achieve these conditions.



There is another option , that would be to implement the functionality for "insert" and "delete" operations into stored procedures which would also check and remove singleton groups when its only user is deleted and also prevent addition of more than one user to the singleton groups






share|improve this answer





















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    Using triggers we can achieve these conditions.



    There is another option , that would be to implement the functionality for "insert" and "delete" operations into stored procedures which would also check and remove singleton groups when its only user is deleted and also prevent addition of more than one user to the singleton groups






    share|improve this answer


























      0














      Using triggers we can achieve these conditions.



      There is another option , that would be to implement the functionality for "insert" and "delete" operations into stored procedures which would also check and remove singleton groups when its only user is deleted and also prevent addition of more than one user to the singleton groups






      share|improve this answer
























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        0






        Using triggers we can achieve these conditions.



        There is another option , that would be to implement the functionality for "insert" and "delete" operations into stored procedures which would also check and remove singleton groups when its only user is deleted and also prevent addition of more than one user to the singleton groups






        share|improve this answer












        Using triggers we can achieve these conditions.



        There is another option , that would be to implement the functionality for "insert" and "delete" operations into stored procedures which would also check and remove singleton groups when its only user is deleted and also prevent addition of more than one user to the singleton groups







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Nov 21 at 4:42









        George Joseph

        1,30249




        1,30249






























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