try: select studentid,max(score) from studentprofile group by studentid; or if you want only those which exists in students select s.studentid,max(p.score) from studentprofile p,students s where s.studentid=p.studentid group by s.studentid; if it takes longer than 1-2 seconds something is seriously wrong Ismo On Tue, 20 Feb 2007, Marko Niinimaki wrote: > Hello, > > I'm having a surprising performance problem with the following simple > 'highscore report' > > select studentid, (select max(score) from > studentprofile prof where prof.studentid = students.studentid) from students; > > I have indexes on students(studentid) and studentprofile(studentid). > > Row counts: about 160 000 in each students and studentprofile. > Postgres version: > postgresql-8.1.8-1.fc5 > postgresql-server-8.1.8-1.fc5 > > This is a dual-processor 3Ghz 64bit box with 2 GB mem. > > Running the query takes 99% CPU and 1% mem. > > I have the same data in MSSQL and there the query takes less than a > minute. With postgres it seems to take several hours. > > Is there a way of making this faster? > > Marko > > ---------------------------(end of broadcast)--------------------------- > TIP 9: In versions below 8.0, the planner will ignore your desire to > choose an index scan if your joining column's datatypes do not > match > >
