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Re: Subquery with range uses filesort
Posted by: Rick James
Date: November 18, 2013 04:33PM

I should emphasize that "filesort" is not the end of the world. It is merely a symptom of a complex query, and it may not be avoidable.

Meanwhile, let's see what we can do for you...

In this
select  *
    from  Player p
    join  History h on h.HistoryPlayer = p.PlayerID
    JOIN  
      ( SELECT  HistoryDate
            from  History
            where  HistoryPlayer = PlayerID
              and  HistoryDate <= '2013-01-01'
            order by  HistoryDate desc, HistoryDirector desc
            limit  0,1 ) x ON x.HistoryDate = h.HistoryDate
"HistoryDirector desc" seems to be unnecessary.

That would let you do MAX(HistoryDate) instead of ORDER BY and LIMIT.

Note that if there are two History rows for a given HistoryDate and PlayerID, the final result will have multiple rows. Is this what you expect?

Hmmm... Now I am confused by "where HistoryPlayer = PlayerID" in the subquery.

What is the query trying to do? Perhaps "find the latest info (from last year) for each player"? If so, then it is a "groupwise max" problem. Search for that.

Could we see the
SHOW CREATE TABLE History;
SHOW CREATE TABLE Players;
It smells like you are missing some indexes.

Notice how this one:
1,PRIMARY,Player,ALL,NULL,NULL,NULL,NULL,53985,100.00,
1,PRIMARY,History,ALL,NULL,NULL,NULL,NULL,880850,100.00,"Using where; Using join buffer"
2,"DEPENDENT SUBQUERY",History,ref,PlayerDateDirector,PlayerDateDirector,4,ratingscentral.Player.PlayerID,8808,100.00,"Using where; Using index; Using filesort"
fails to use any indexes. In fact it does a cross-join between Player and History before touching the _dependent_ subquery. That should take a looong time.

You have an awful number of indexes on Player. Most of them are probably not worth having.

Sorry, I don't (yet) have the answers you want.

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