从同一表的两列到同一主键的外键

Question

I have two tables:

users

id  |  username
--------------
 1  |  James
 2  |  John
 3  |  Jack
 4  |  Jim
 5  |  Jane
 6  |  Jessica

juniors

senior_id  |  junior_id
-----------------------
 1         |  4
 1         |  6
 2         |  3
 4         |  5

Both the senior_id and junior_id refer to the users table's id column.

How do I set it up so that a) it is guaranteed that both senior_id and junior_id exist in users and b) a delete from users will cascade and remove any instances of the deleted id from juniors whether it's a senior_id or junior_id ? Ie deleting Jim in the example above will automatically remove both the first and last record from juniors.

I tried doing this with two separate constraints. But if I set up cascade on both constraints I get a 'may cause cycles or multiple cascade paths' error.

And if I set it on only one constraint then a delete fails (in a case like Jim) because it cascades to only one of the columns and thus then violates the constraint.

I have to be able to do this on SQL Server 2005.

Answer 1

Remove FK constraint.For FK constraint check.Create trigger on table juniors before insert/update.if id do not exists then rollback.Again now create another trigger on table User for DELETE.and in trigger write script to delete all record.since FK do not fulfill your requirement,therefore no point in keeping one extra constraint.

Most importantly I think your table design is bad.Table design should be like Employee-Manager relation table ie keep SeniorID in User Table itself.

so many of your problem will vanish . Also there is no extra cost or complication for any query on this table

id  |  username   SeniorID
--------------
 1  |  James
 2  |  John
 3  |  Jack        2
 4  |  Jim         5 
 5  |  Jane
 6  |  Jessica