[SQL] SELECT DISTINCT too slow

[Miroslav Šulc]

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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