Hi, I hope this is the best place to report this or should I be on pgsql-general or pgsql-bugs?
It seems that the order of columns in a query can make a difference in execution times. In my brief investigation, queries on table(a,b,c,d,e,f,g,h) of the form select * from table order by non-indexed-column limit 25; select a,b,c,d,e,f,g,h from table order by non-indexed-column limit 25; performed the same (approx 1.5 seconds on our customers table -- rows=514431 width=215), while the query select h,g,f,e,d,c,b,a from table order by non-indexed-column limit 25; was about 50% slower (approx 2.2 seconds on our customers table). I had expected these to perform the same -- to my mind column ordering in a query should be purely presentation -- as far as I'm concerned, the DBMS can retrieve the columns in a different order as long as it displays it in the order I've asked for them. Although, again, the order of columns in a resultset in a Java or Python is mostly irrelevant, though when displayed in psql I'd want the columns in the order I asked for them. Is there really something strange happening here? Or perfectly explainable and expected? Regards, Colin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
