I have a very simple SQL query:
SELECT COUNT(DISTINCT x) FROM table;
My table has about 1.5 million rows. This query is running pretty slowly; it takes about 7.5s, compared to
SELECT COUNT(x) FROM table;
which takes about 435ms. Is there any way to change my query to improve performance? I've tried grouping and doing a regular count, as well as putting an index on x; both have the same 7.5s execution time.
\d
output ofpsql
is good one) and precise the column that you have problem with. It'd be good to seeEXPLAIN ANALYZE
of both queries. – vyegorov