slow join on table (10k rows) - mysql

Question

i have table actions (30 rows) and passed_actions(10k rows)
actions table:
CREATE TABLE `actions` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`category_id` int(10) unsigned NOT NULL,
`author_id` int(10) unsigned NOT NULL,
`name` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`slug` varchar(255) COLLATE utf8_unicode_ci NOT NULL COMMENT 'need for url',
`about` longtext COLLATE utf8_unicode_ci,
`image` text COLLATE utf8_unicode_ci,
`page_title` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`page_description` varchar(512) COLLATE utf8_unicode_ci DEFAULT NULL,
`active` tinyint(1) NOT NULL DEFAULT '0',
`created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
UNIQUE KEY `actions_slug_unique` (`slug`),
KEY `actions_author_id_foreign` (`author_id`),
KEY `actions_category_id_foreign` (`category_id`),
CONSTRAINT `actions_author_id_foreign` FOREIGN KEY (`author_id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `actions_category_id_foreign` FOREIGN KEY (`category_id`) REFERENCES `categories` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=38 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
and passed_actions (~9500 rows)
CREATE TABLE `passed_actions` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`user_id` int(10) unsigned NOT NULL,
`action_id` int(10) unsigned NOT NULL,
`hash` varchar(6) COLLATE utf8_unicode_ci NOT NULL,
`public` tinyint(1) NOT NULL DEFAULT '1',
`successfully_passed` tinyint(1) NOT NULL DEFAULT '0',
`started_at` timestamp NULL DEFAULT NULL,
`created_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
UNIQUE KEY `passed_actions_hash_unique` (`hash`),
KEY `passed_actions_user_id_foreign` (`user_id`),
KEY `passed_actions_action_id_foreign` (`action_id`),
CONSTRAINT `passed_actions_action_id_foreign` FOREIGN KEY (`action_id`) REFERENCES `actions` (`id`) ON DELETE CASCADE,
CONSTRAINT `passed_actions_user_id_foreign` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=25733 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
this query takes 0.3-0.5s:
select
actions.*
from actions
left join passed_actions.action_id = actions.id
group by actions.id
order by count(passed_actions.id) DESC
this affects to response time of my api...
why is this happening? i think that 10k rows is not a large table...
i use default mysql config. My server is 1gb ram and 1 cpu (digital ocean droplet)

Answer 1

Your query is actually reasonable fast. Sometimes a correlated subquery can help:
select a.*
from actions a
order by (select count(*) from passed_actions pa where pa.action_id = a.id) desc;
This can use the index you have defined on passed_actions(action_id).

Answer 2

If all you want off the second table is the count for sorting, as appears to be the case, try (untested, sorry):
select
actions.*
from actions
left join (select action_id, count(*) as passed_count from passed_actions group by action_id) p on actions.action_id = p.action_id
order by passed_count DESC
(I can't see where tests.id is coming from, I'm afraid.)

Answer 3

1- Rebuild the index and update statistics
2- Select Only the column you want to use
3- run this query in a new query and hit "Right click" and Click on "Display Estimated Execution Plan" and view the Missing Index Details and build the required index and run the query again