I have rather large table with about 5 millions of rows and a dozen of
columns. Let's suppose that columns are named 'a', 'b', 'c' etc. I need
to query distinct pairs of ('a';'b') from this table.
I use following query:
SELECT DISTINCT a, b FROM tbl;
but unfortunately, it takes forever to complete. Explaining gives me
information that bottleneck is seqscan on 'tbl', which eats much time.
Creating compound index on this table using following statement:
CREATE INDEX tbl_a_b_idx ON tbl( a, b );
gives no effect, postgres simply ignores it, at least according to the
Is there any way to somehow improve the performance of this operation?
Table can not be changed.
Internal Development Engineer
pgsql-performance by date
|Next:||From: Richard Huxton||Date: 2007-01-30 09:12:51|
|Subject: Re: Querying distinct values from a large table|
|Previous:||From: Tomas Vondra||Date: 2007-01-30 07:10:14|
|Subject: Re: Partitioning|