18.06.2012 11:37, lacakus wrote: > > I guess, that it is because COALESCE is internaly transformed into CASE > WHEN <subselect> IS NULL then 0 else <subselect> end > So in expression is subselect twice.
Correct. > My question is if <subselect> is really executed twice for every row in > table1? or is there internal optimization where duplicate expressions > are reduced? Optimization happens only in Firebird 2.5 and above: http://tracker.firebirdsql.org/browse/CORE-501 Dmitry
