Re: Slow COUNT + GROUP BY

[Øystein Grøvlen]

Hi,

AFAICT, your query is equivalent to the following query:

SELECT COUNT(DISTINCT uids) FROM unique_playing
WHERE day BETWEEN "2013-03-01 00:00:00.000" AND "2015-03-18 00:00:00.000";

FORCE INDEX(PRIMARY) should normally not be beneficial unless most of your records are within the given the date period. I suspect the problem is that the index on day is not used for some reason. What type is your day column? SHOW CREATE TABLE for the table and EXPLAIN output for the query (without FORCE INDEX) should probably tell us more.

What storage engine are you using, InnoDB or MyISAM? What version of MySQL?

Øystein Grøvlen,
Senior Principal Software Engineer,
MySQL Group, Oracle,
Trondheim, Norway