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Home » Performance » MySQL » Simple LEFT JOIN still uses file sort
Simple LEFT JOIN still uses file sort [message #551] Mon, 08 January 2007 19:28 Go to previous message
Niels is currently offline Niels
Messages: 2
Registered: January 2007
Junior Member
Hi!

I'm using a very simple JOIN:

SELECT *
FROM A
LEFT JOIN B ON A.pointer=B.id
ORDER BY A.id;

EXPLAIN tells me it uses file sort. There are indexes on all fields. The problem is the ORDER, but I don't fully understand why this situation causes problems.

I use this kind of query a lot in a webapp I'm doing, and for small tables it's fine. But with 100k records in A and B, it becomes unusable. Maybe I could fine tune a cache or two, but that doesn't really solve the problem. Can it really be that it's impossible to do this without file sort?


Thanks,
Niels
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