On Wed, 19 Nov 2008, [ISO-8859-5] ²öâÐÛöÙ ÂØÜçØèØÝ wrote: > Query 1: > select * from t1 where id not in (select id from t2); > > Query 2 (gives same result as Q1): > select * from t1 except all (select id from t2); It gives the same result as long as no nulls are in either table. If either table can have a null, the conversion changes the results. In addition, a conversion like the above only happens to work because t1 only has an id column. If t1 had two columns you'd get an error because the two sides of except all must have the same number of columns. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
