> I use a similar SQL, e.g.: > select func(x)....group by func(x) order by func(x) > but my func is rather expensive. Is func(x) evaluated three times > in the above statement? Would it be evaluated only once if I used > select func(x)....group by 1 order by 1 try: select q.v from (select func(t.x) as v from t) q order group by 1 order by 1; Is your function immutable? You have to be very careful with expensive functions in the select clause. for example select f(x) from t where id = 1 order by n; can cause f to execute for the entire table even if id is unique. Solution is to subquery as in the above. merlin
