On Sat, Jun 28, 2008 at 06:24:42PM +0200, Moritz Onken wrote: > SELECT distinct url from item where url like 'http://www.micro%' limit > 10;
Here, the planner knows the pattern beforehand, and can see that it's a simple prefix. > select * > from result > where exists > (select * from item where item.url LIKE result.url || '%' limit 1) > limit 10; Here it cannot (what if result.url was '%foo%'?). Try using something like (item.url >= result.url && item.url <= result.url || 'z'), substituting an appropriately high character for 'z'. > The only explaination is that I don't use a constant when comparing the > values. But actually it is a constant... It's not a constant at planning time. Also note that you'd usually want to use IN instead of a WHERE EXISTS. /* Steinar */ -- Homepage: http://www.sesse.net/ -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
