2009/8/20 Dmitry Samokhin <s...@mail.ru>: > > The following bug has been logged online: > > Bug reference: 4997 > Logged by: Dmitry Samokhin > Email address: s...@mail.ru > PostgreSQL version: 8.3.7 > Operating system: Windows 2003 Server > Description: Expression evaluation rules > Details: > > As described in section "4.2.12. Expression Evaluation Rules" in the > documentation, "the order of evaluation of subexpressions is not defined", > and the proposed solution is to use the CASE statement. Consider the > following query: > > SELECT CASE WHEN TRUE THEN TRUE ELSE 1 / 0 = 1 END; > > It returns 'TRUE' as expected, I don't see the 'division by zero' error, so > the ELSE branch is not evaluated at all. > > Then, consider this test case: > > -- Start of DDL script > > CREATE OR REPLACE FUNCTION trg_mytable_after() > RETURNS trigger AS > $BODY$ > BEGIN > IF TG_OP = 'UPDATE' OR TG_OP = 'DELETE' THEN > IF (CASE WHEN TG_OP = 'DELETE' THEN TRUE ELSE OLD.a <> NEW.a END) THEN > RAISE NOTICE 'OK!'; > END IF; > END IF; > > RETURN NULL; > END; > $BODY$ > LANGUAGE 'plpgsql' VOLATILE > COST 100; > > CREATE TABLE mytable > ( > a integer NOT NULL, > CONSTRAINT pk_mytable PRIMARY KEY (a) > ) > WITH ( > OIDS=FALSE > ); > > CREATE TRIGGER trg_mytable_after > AFTER INSERT OR UPDATE OR DELETE > ON mytable > FOR EACH ROW > EXECUTE PROCEDURE trg_mytable_after(); > > -- End of DDL script > > INSERT INTO mytable (a) VALUES (1); > DELETE FROM mytable WHERE a = 1; > > On DELETE statement, the error occurs: > > ERROR record "new" is not assigned yet > DETAIL The tuple structure of a not-yet-assigned record is indeterminate > > So it seems although (TG_OP = 'DELETE') is TRUE, the ELSE branch of the CASE > statement (OLD.a <> NEW.a) in the trigger procedure is still evaluated. > > -- > Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-bugs >
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