From: Miroslav Šulc <miroslav.sulc@startnet.cz>
To: pgsql-sql@postgresql.org
Subject: SELECT DISTINCT too slow
Date: Thu, 01 Jun 2006 15:26:09 +0200
Message-ID: <447EEAF1.7040305@startnet.cz> (raw)
Hello,
I have a table with cca 400,000 rows. The table contains column "key" of
varchar(20) type containing 10 distinct values. I want to get out what
distinct values are present in the column. I use this simple query,
which is very slow:
SELECT DISTINCT Key FROM MRTPContactValue
Here is the query plan:
QUERY PLAN
Unique (cost=64882.26..66964.59 rows=9 width=9) (actual time=26139.972..29593.164 rows=10 loops=1)
-> Sort (cost=64882.26..65923.43 rows=416466 width=9) (actual time=26139.964..27975.944 rows=416466 loops=1)
Sort Key: "key"
-> Seq Scan on mrtpcontactvalue (cost=0.00..8669.66 rows=416466 width=9) (actual time=0.026..2460.535 rows=416466 loops=1)
Total runtime: 29603.159 ms
I've tried index on the "key" column but no improvement.
Is there a way to speed the SELECT up?
Thank you for any suggestions.
--
Miroslav Šulc
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Subject: Re: SELECT DISTINCT too slow
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