Comments on: MySQL Performance – eliminating ORDER BY function

By: Karl Ravn

Karl Ravn — Fri, 06 Mar 2009 00:08:29 +0000

And, if anyone skipped the fine prints in the docs, you can also remove the whole order by-clause, making indexed scans alot faster if the result is rather large, and the order of the rows doesn’t matter. For example statistics or samples of rows. just type ORDER BY NULL (unsure of ansi-compatibility though).. Then the result will be in the order that they are in the database (based on creation, unless you have deleted rows). Even small queries can ease some load on a heavy-traffic db server with this technique.

By: techblog.tilllate.com » Peter Zaitsev of the MySQL Performance Blog speaks in Zurich-

Sun, 18 Nov 2007 18:29:19 +0000

[...] about MySQL performance optimization. He and his partners of Percona write about topics like eliminating ORDER BY function or Be careful when joining on CONCAT. Peter also held presentations at all Mysql Conferences. In [...]

By: peter

peter — Thu, 01 Nov 2007 22:56:34 +0000

Why are you surprised you’re sorting by FIELD function – of course MySQL can’t use Index to do such sort.

By: Ladislav

Ladislav — Thu, 01 Nov 2007 18:43:18 +0000

Sorry, something’s missing … the problem is the filesort, of course

By: Ladislav

Ladislav — Thu, 01 Nov 2007 18:40:57 +0000

Slightly off-topic: talking about order by … trying to find solution for a long time to optimize queries with “order by field” like this:

EXPLAIN SELECT id, name
FROM table_name
WHERE id IN ( 222839, 299872, 301535 )
ORDER BY FIELD( id, 222839, 299872, 301535 )

FROM EXPLAIN:
—————————————
select_type SIMPLE
table table_name [innodb]
type range
possible_keys PRIMARY
key PRIMARY
key_len 4
ref NULL
rows 3
Extra Using where; Using filesort

Am I plain stupid or is it a bug (in the optimizer) in MySQL ?

By: Lukas

Lukas — Wed, 17 Oct 2007 13:04:58 +0000

So the lesson to learn is if you always apply a specific function on a column, you might as well apply it before the actual insert so that you can leverage the index properly. Or denormalize ..