Re: Transactions within a function body

Hi.

My humble opinion follows.

One point here is that the decision for the ROLLBACK could possibly be
different from errors.
It could simply be based upon a generic expression, not just the conditions
seen in "Appendix A" of the manual.
An exception is something different from a transaction, despite the former is
implemented with the latter.

On Thursday 02 October 2008 11:53:17 Richard Huxton wrote:
> Albe Laurenz wrote:
> > After a discussion on comp.databases.postgresql I realized that this
> > is actually a limitation.
> >
> > Consider the following:
> >
> > BEGIN
> > UPDATE ...
> > UPDATE ...
> > UPDATE ...
> > EXCEPTION
> > WHEN integrity_constraint_violation THEN
> > ...
> > END;
> >
> > If the first UPDATE succeeds but the second one bombs, there is no way
> > to undo the first update short of having the whole transaction cancelled.
>
> No, I think you've got that backwards Albe. You can even nest exceptions.
>
> > If you need all three of these UPDATEs to either all succeed or fail,
> > but the whole transaction should continue, you cannot do that in
> > PL/pgSQL.
>
> Try the following script. By commenting out the second INSERT you can
> change whether you get one or no rows inserted into t1. The
> BEGIN...EXCEPTION...END block has a savepoint set at the "BEGIN".
>
>
> BEGIN;
>
> CREATE TABLE t1 (a integer);
>
> CREATE OR REPLACE FUNCTION test_exception()
> RETURNS boolean AS $$
> DECLARE
> n integer;
> BEGIN
> INSERT INTO t1 (a) VALUES (1);
> -- INSERT INTO t1 (a) VALUES ('b');
> BEGIN
> INSERT INTO t1 (a) VALUES (2);
> INSERT INTO t1 (a) VALUES ('c');
> EXCEPTION
> WHEN OTHERS THEN
> SELECT INTO n count(*) FROM t1;
> RAISE NOTICE 'n2 = %', n;
> RETURN false;
> END;
> RETURN true;
> EXCEPTION
> WHEN OTHERS THEN
> SELECT INTO n count(*) FROM t1;
> RAISE NOTICE 'n1 = %', n;
> RETURN false;
> END;
> $$ LANGUAGE plpgsql;
>
> SELECT test_exception();
>
> SELECT count(*) FROM t1;
>
> ROLLBACK;