Royce Ausburn <royce.ml@xxxxxxxxxxx> writes: > [ random() is evaluated only once in ] > test=# select (select random()) from generate_series(1,10); -- rows are the same > I understand that it's likely an optimisation thing -- postgres knows > that the subselect doesn't depend on the FROM rows so it evaluates it > only once, but is this really correct behaviour? I can't find anything in the SQL standard that explicitly addresses this point, but a bit of googling turns up documentation for both Oracle and DB/2 that say they evaluate uncorrelated subqueries just once: http://www.smart-soft.co.uk/Oracle/advanced-sql-tutorial.htm http://publib.boulder.ibm.com/infocenter/iseries/v5r3/index.jsp?topic=/sqlp/rbafycorrs.htm whereas correlated subqueries are evaluated once per row. So we're in good company here. Even if we were not, I'd be loath to change it, because people have historically relied on this behavior to force single evaluation of what otherwise would be considered volatile functions. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
