MySQL Query is slow (Joins/counts) - mysql

Question

I have this query:
SELECT `assemblies`.`id`,
`assemblies`.`type`,
`assemblies`.`champion`,
`assemblies`.`name`,
`assemblies`.`author`,
`assemblies`.`githublastmod`,
( assemblies.forum IS NOT NULL ) AS forumExists,
Count(votes.id) AS votesCount,
Count(install_clicks.id) AS installCount,
Count(github_clicks.id) AS githubCount,
Count(forum_clicks.id) AS forumCount
FROM `assemblies`
INNER JOIN `votes`
ON `votes`.`assembly` = `assemblies`.`id`
INNER JOIN `install_clicks`
ON `install_clicks`.`assembly` = `assemblies`.`id`
INNER JOIN `github_clicks`
ON `github_clicks`.`assembly` = `assemblies`.`id`
INNER JOIN `forum_clicks`
ON `forum_clicks`.`assembly` = `assemblies`.`id`
WHERE `assemblies`.`type` = 'utility'
AND Unix_timestamp(Date(assemblies.githublastmod)) > '1419536536'
GROUP BY `assemblies`.`id`
ORDER BY `votescount` DESC,
`githublastmod` DESC
For some reason this query is very slow, I'm using the database engine MyISAM. I hope someone can help me out here :)
Explain command:

Answer 1

I believe this is a case where making the subqueries for the counts will make it run a lot faster (and the values will be correct).
The problem with the original query is the explosion of the number of intermediate rows: For each 'assembly', there were n1 votes, n2 installs, etc. That led to n1*n2*... rows per assembly.
SELECT `assemblies`.`id`, `assemblies`.`type`, `assemblies`.`champion`,
`assemblies`.`name`, `assemblies`.`author`, `assemblies`.`githublastmod`,
( assemblies.forum IS NOT NULL ) AS forumExists,
( SELECT Count(*)
FROM votes
WHERE `assembly` = `assemblies`.`id`
) AS votesCount,
( SELECT Count(*)
FROM install_clicks
WHERE `assembly` = `assemblies`.`id`
) AS installCount,
( SELECT Count(*)
FROM github_clicks
WHERE `assembly` = `assemblies`.`id`
) AS githubCount,
( SELECT Count(*)
FROM forum_clicks.id
WHERE `assembly` = `assemblies`.`id`
) AS forumCount
FROM `assemblies`
WHERE `assemblies`.`type` = 'utility'
AND Unix_timestamp(Date(assemblies.githublastmod)) > '1419536536'
ORDER BY `votescount` DESC, `githublastmod` DESC
Each secondary table needs an INDEX starting with assembly.

Answer 2

Your problem should be fixed using the right indices:
CREATE INDEX index_name_1 ON `votes`(`assembly`);
CREATE INDEX index_name_2 ON `install_clicks`(`assembly`);
CREATE INDEX index_name_3 ON `github_clicks`(`assembly`);
CREATE INDEX index_name_4 ON `forum_clicks`(`assembly`);
Try your query again after creating these indices and it should be quite faster.