Re: Enforcing Join condition

சிவகுமார் மா wrote:
> CREATE TABLE test (info_type varchar(3), info_reference integer);
> (depending on info_type, info_reference will contain key values from
> different tables)
> 
> INSERT INTO test (info_type, info_reference) values ('abc','111'); ---
> 111 from tableA
> INSERT INTO test (info_type, info_reference) values ('def','101');
> --- 101 from tableB
> INSERT INTO test (info_type, info_reference) values ('abc','119'); ---
> 119 from tableA
> INSERT INTO test (info_type, info_reference) values ('def','103');
> --- 103 from tableB
> INSERT INTO test (info_type, info_reference) values ('def','104');
> --- 104 from tableB
> INSERT INTO test (info_type, info_reference) values ('def','105');
> --- 105 from tableB
> INSERT INTO test (info_type, info_reference) values ('def','111');
> --- 111 from tableB
> 
> Now when joining tableA or tableB with test, joining only
> info_reference will be wrong, we should also mention the info_type
> value.
> 
> 1. Is this an appropriate design for this requirement?
> 2. Is there a way to enforce the dual condition checking on all
> queries. If a join is made to info_reference, info_type should also be
> specified?

I think I understand:

You want to have a "conditional" foreign key reference that checks
against different tables depending on a "type" field, right?

For complicated conditions like this, you could use a
BEFORE INSERT trigger that throws an error when the condition
is violated.

Yours,
Laurenz Albe