Uniqueness constraint based on column value in a related table
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
asked Nov 21 '18 at 2:05
vasilyvasily
1,6011326
add a comment |
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
asked Nov 21 '18 at 2:05
vasilyvasily
1,6011326
1
Handling both these requirements is probably best accomplished with triggers.
– Gordon Linoff
Nov 21 '18 at 3:09
add a comment |
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
asked Nov 21 '18 at 2:05
vasilyvasily
1,6011326
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
mysql sql
asked Nov 21 '18 at 2:05
vasilyvasily
1,6011326
asked Nov 21 '18 at 2:05
vasilyvasily
1,6011326
asked Nov 21 '18 at 2:05
vasilyvasily
1,6011326
asked Nov 21 '18 at 2:05
vasilyvasily
1,6011326
asked Nov 21 '18 at 2:05
vasilyvasily
1,6011326
1,6011326
1
Handling both these requirements is probably best accomplished with triggers.
– Gordon Linoff
Nov 21 '18 at 3:09
add a comment |
1
Handling both these requirements is probably best accomplished with triggers.
– Gordon Linoff
Nov 21 '18 at 3:09
1
1
Handling both these requirements is probably best accomplished with triggers.
– Gordon Linoff
Nov 21 '18 at 3:09
Handling both these requirements is probably best accomplished with triggers.
– Gordon Linoff
Nov 21 '18 at 3:09
add a comment |
1 Answer
1
active
oldest
votes
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
answered Nov 21 '18 at 4:42
George JosephGeorge Joseph
1,44249
add a comment |
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active
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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
answered Nov 21 '18 at 4:42
George JosephGeorge Joseph
1,44249
add a comment |
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
answered Nov 21 '18 at 4:42
George JosephGeorge Joseph
1,44249
add a comment |
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
answered Nov 21 '18 at 4:42
George JosephGeorge Joseph
1,44249
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
answered Nov 21 '18 at 4:42
George JosephGeorge Joseph
1,44249
answered Nov 21 '18 at 4:42
George JosephGeorge Joseph
1,44249
answered Nov 21 '18 at 4:42
George JosephGeorge Joseph
1,44249
answered Nov 21 '18 at 4:42
George JosephGeorge Joseph
1,44249
1,44249
add a comment |
add a comment |
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Handling both these requirements is probably best accomplished with triggers.
– Gordon Linoff
Nov 21 '18 at 3:09