> Is it ALWAYS possible to fabricate a query/schema in
> such a way that MySQL ALWAYS uses the ideal
No. Optimisation is better in 5.6 than in 5.0, though.
Did you try adding multi-column indexes to cover the join and the order
by clause?
> 'Using where' extra -- you just have to keep at it?
> Or is it the case that sometimes you're just S.O.L
I don't know a general answer to that question. To figure out the answer
in a particular case, I usually have to see the Create Table statements,
see how the query performs with representative data, and experiment with
various index setups.
PB
-----
On 5/31/2011 1:27 PM, Daevid Vincent wrote:
I sent this Friday, but it never made it to the list?!
-----Original Message-----
From: Daevid Vincent [mailto:dae...@daevid.com]
Sent: Friday, May 27, 2011 12:27 PM
To: mysql@lists.mysql.com
Subject: Using where; Using temporary; Using filesort
I'm trying to optimize a query that doesn't seem all that complicated,
however I can't seem to get it to not use a temp table and filesort.
developer@vm_vz_daevid:~$ mysql --version
mysql Ver 14.12 Distrib 5.0.92, for portbld-freebsd8.1 (amd64) using 5.2
EXPLAIN EXTENDED
SELECT
-- d.date_release,
-- d.dvd_title,
-- s.type,
-- s.id_place,
s.scene_id AS index_id,
s.dvd_id
FROM
dvds AS d JOIN scenes_list AS s
ON s.dvd_id = d.dvd_id
AND d.status = 'ok'
AND d.date_release != '0000-00-00'
ORDER BY d.date_release DESC,
d.dvd_title ASC,
s.type ASC,
s.id_place ASC;
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: d
type: ref
possible_keys: PRIMARY,date_release,status,status_release
key: status_release
key_len: 1
ref: const
rows: 1976
Extra: Using where; Using temporary; Using filesort
*************************** 2. row ***************************
id: 1
select_type: SIMPLE
table: s
type: ref
possible_keys: dvd_id_2,dvd_id
key: dvd_id
key_len: 4
ref: videoszcontent.d.dvd_id
rows: 6
Extra: Using where
2 rows in set, 1 warning (0.00 sec)
There are proper indexes on most every column in both tables (as you can see
there).
[a] the EXTENDED keyword doesn't seem to do anything different? I get the
same columns and results??!
[b] The commented out columns above I thought might help with the ORDER BY
for some reason from my reading here:
http://dev.mysql.com/doc/refman/5.0/en/order-by-optimization.html
they did not.
[c] lopping off the ORDER BY all together stops the "Using temporary; Using
filesort" of course. Yeah! But now I'm left with a table of data in random
order. Re-sorting it in PHP seems like an even bigger waste of cycles, when
no doubt MySQL can sort hella-faster.
[d] just doing " ORDER BY d.date_release DESC, d.dvd_title ASC; ", prevents
the "using temporary" but still does "filesort" and again I'm in the boat of
[c]
I guess my question is this: Is it ALWAYS possible to fabricate a
query/schema in such a way that MySQL ALWAYS uses the ideal 'Using where'
extra -- you just have to keep at it? Or is it the case that sometimes
you're just S.O.L. and no matter what, MySQL is going to give you a
Cleveland Steamer? In other words, am I wasting my time trying to tweak my
query and indexes here with the idea there's some magic incantation that
will get this "right" or do I just have to accept it is what it is and it's
not going to do any better.
d.
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