I have the following tables (All InnoDb):
CREATE TABLE `user` (
`id` BIGINT(20) NOT NULL AUTO_INCREMENT,
`num` INT(11) NOT NULL,
`date` DATETIME NOT NULL DEFAULT '2014-01-01 00:00:00',
`year` VARCHAR(4) NOT NULL DEFAULT '1999',
PRIMARY KEY (`id`),
INDEX `yearIDX` (`year`, `num`),
INDEX `date` (`year`, `date`),
INDEX `dateonly` (`date`),
)
CREATE TABLE `log` (
`id` BIGINT(20) NOT NULL AUTO_INCREMENT,
`unit_id` BIGINT(20) NULL DEFAULT NULL
PRIMARY KEY (`id`),
INDEX `logunitIDX` (`unit_id`),
CONSTRAINT `logunitIDX` FOREIGN KEY (`unit_id`) REFERENCES `unit` (`id`)
)
CREATE TABLE `user_log` (
`user_id` BIGINT(20) NOT NULL,
`log_id` BIGINT(20) NOT NULL,
`user_log_idx` INT(11) NOT NULL,
PRIMARY KEY (`user_id`, `user_log_idx`),
INDEX `user_log_key` (`user_id`),
INDEX `user_log` (`log_id`),
INDEX `Index 4` (`user_id`, `log_id`, `user_log_idx`),
CONSTRAINT `user_log` FOREIGN KEY (`log_id`) REFERENCES `log` (`id`),
CONSTRAINT `user_log_key` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`)
)
CREATE TABLE `unit` (
`id` BIGINT(20) NOT NULL AUTO_INCREMENT,
`code` SMALLINT(6) NOT NULL
PRIMARY KEY (`id`),
UNIQUE INDEX `codeIDX_U` (`code`)
)
And the following query
SELECT
user0_.id AS e1_26_,
user0_.`num` AS registry4_26_,
user0_.`date` AS date5_26_
FROM `user` user0_
INNER JOIN `user_log` userlog1
ON user0_.id=userlog1.`user_id`
INNER JOIN `log` userlo2
ON userlog1.`log_id`=userlo2.id
INNER JOIN `unit` unit3_
ON userlo2.`unit_id`=unit3_.id
WHERE
user0_.`year`='2014'
AND
(unit3_.`code` in ('41','42','43','45'))
ORDER BY user0_.`date` DESC
LIMIT 400
The query analyser shows this (for brevity I omit select_type and key_len. select_type is SIMPLE)
id table type possible_keys key ref rows Extra
1 unit3_ range PRIMARY,
codeIDX_U codeIDX_U Null 10 Using where;
Using index;
Using temporary;
Using filesort
1 userlo2 ref PRIMARY,
logunitIDX,
Index 6 logunitIDX unit3_.id 1194 Using where;
Using index
1 userlog1 ref PRIMARY,
user_log_key,
user_log,
Index 4 user_log userlo2.id 1 Using index
1 user0_ eq_ref PRIMARY,
yearIDX,
date PRIMARY userlog1.user_id 1 Using where
I believe that the reason that I get a "Using temporary; Using filesort" in the first line is because "I am joining many tables and the columns in the ORDER BY" are not from the first non-constant tables to retrieve rows"
Does anyone have any idea if this query can be optimised to not use temp/filesort?
Everything you are selecting is from user0_
, so you appear to be using the join
s for filtering. Assuming that you do not care about multiple rows, you can rewrite the query using exists
. This might allow the optimizer to get rid of the file sort:
SELECT u0.id AS e1_26_, u0.`num` AS registry4_26_, u0.`date` AS date5_26_
FROM `user` u0
WHERE EXISTS (SELECT 1
FROM `user_log` userlog1 INNER JOIN
`log` userlo2
ON userlog1.`log_id`= userlo2.id INNER JOIN
`unit` unit3_
ON userlo2.`unit_id`= unit3_.id
WHERE u0.id = userlog1.`user_id` AND
unit3_.`code` in ('41', '42', '43', '45')
) AND
u0.`year` = '2014'
ORDER BY u0.`date` DESC
LIMIT 400;
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