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01.23.2008 at 10:57AM PST, ID: 23105429
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MySQL Query optimization with a join and group by

Asked by MacAnthony in MySQL

Tags: SQL

I have a relatively simple query that uses a join and a group by but the query takes a while to run. The first table has 45k rows and the joined table has 5k rows and without query caching, it takes about 2 seconds to run on our development server. Without the group by, it takes about 11ms. There are individual indexes applied to all the references columns but no multicolumn indexes (I'm not real good at figuring out what the indexes should be).

I've attached the query and the explain statement.Start Free Trial 
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QUERY:
SELECT SQL_NO_CACHE `t1`.`tasklistCompletionId` AS `tasklistCompletionId` , max( `t2`.`lastModified` ) AS `revUsedDate` , `t2`.`tasklistItemId` AS `tasklistItemId`
FROM (
`tasklistCompletion` `t1`
JOIN `tasklistItem` `t2` ON (
`t1`.`tasklistItemId` = `t2`.`tasklistItemId`
AND `t2`.`lastModified` <= `t1`.`completionDate`
)
)
GROUP BY `t1`.`tasklistCompletionId`
 
 
 
EXPLAIN:
id 	select_type 	table 	type 	possible_keys 	key 	key_len 	ref 	rows 	Extra
1 	SIMPLE 	t2 	ALL 	lastModified,tasklistItemId 	NULL 	NULL 	NULL 	4769 	Using temporary; Using filesort
1 	SIMPLE 	t1 	ref 	checklistItemId,completionDate 	checklistItemId 	4 	projects.t2.tasklistItemId 	3 	Using where
 
Keywords: MySQL Query optimization with a join a…
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[+][-]01.23.2008 at 11:33PM PST, ID: 20731396

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[+][-]01.24.2008 at 05:36AM PST, ID: 20732794

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About this solution

Zone: MySQL
Tags: SQL
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Solution Provided By: AdrianSRU
Participating Experts: 2
Solution Grade: A
 
 
[+][-]01.24.2008 at 05:44AM PST, ID: 20732868

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[+][-]01.24.2008 at 06:48AM PST, ID: 20733412

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[+][-]01.24.2008 at 07:13AM PST, ID: 20733689

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[+][-]01.24.2008 at 07:31AM PST, ID: 20733871

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[+][-]01.24.2008 at 07:32AM PST, ID: 20733883

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