Обсуждение: Testing Inserts, Deletes and Updates before execution ...

Dear list,

i am looking for a way to check, whether an DML-statement can be
performed on a current database. That means, that i want to check, if
e.g. an INSERT is possible or not (due to existing constraints), without
executing it.

Any ideas?

Hagen

Hagen Hoepfner wrote:

> i am looking for a way to check, whether an DML-statement can be
> performed on a current database. That means, that i want to check, if
> e.g. an INSERT is possible or not (due to existing constraints), without
> executing it.

I think this could be the easiest way: try it and rollback.

BEGIN;
SET CONSTRAINTS ALL IMMEDIATE; -- if you have deferred foreign key, e.g.
INSERT .... -- check if it works
ROLLBACK;

That should do what you want, IMHO.
In PostgreSQL 8.0 you would not need your own transaction here...

BEGIN;
-- do some work

SAVEPOINT check_dml;
INSERT ... -- check if it works
ROLLBACK TO check_dml;

-- do some more work
COMMIT;

Could this be what you want?

Best Regards,
Michael Paesold