> -----Mensaje original----- > De: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] En nombre de Patrick > Scharrenberg > Enviado el: Martes, 17 de Junio de 2008 17:46 > Para: pgsql-sql@postgresql.org > Asunto: [SQL] using calculated column in where-clause > > Hi! > > I'd like to do some calculation with values from the table, > show them a new column and use the values in a where-clause. > > Something like this > select a, b , a*b as c from ta where c=2; > > But postgresql complains, that column "c" does not exist. > > Do I have to repeat the calculation (which might be even more complex > :-) ) in the "where"-clause, or is there a better way? >
For complex calculations I have obtained better performance using nested queries. For example: select a, b, c select ( select a, b, a*b as c from ta) subquery1 where c = 2; This nesting is probably overhead in such a simple case as this, but in more complex ones and specially with volatile functions it will provide an improvement. Regards, Fernando. -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
