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POHow to Optimize a Query With GROUP BY and ORDER BY
 

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    <p>I have got a <code>POSTS</code> table, the structure is like this:</p> <pre><code>CREATE TABLE IF NOT EXISTS `posts` ( `id` int(11) NOT NULL AUTO_INCREMENT, `title` varchar(255) COLLATE utf8_turkish_ci DEFAULT NULL, `content` longtext COLLATE utf8_turkish_ci, `excerpt` longtext COLLATE utf8_turkish_ci, `link` longtext COLLATE utf8_turkish_ci, `original_link` longtext COLLATE utf8_turkish_ci, `mime_type` longtext COLLATE utf8_turkish_ci, `language_id` int(11) DEFAULT NULL, `user_id` int(11) DEFAULT NULL, `site_id` int(11) DEFAULT NULL, `type` varchar(255) COLLATE utf8_turkish_ci DEFAULT NULL, `created_at` datetime DEFAULT NULL, `modified_at` datetime DEFAULT NULL, `is_deleted` int(11) DEFAULT NULL, PRIMARY KEY (`id`), KEY `user_id` (`user_id`), KEY `type` (`type`), KEY `created_at` (`created_at`), ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_turkish_ci AUTO_INCREMENT=52487 ; </code></pre> <p>And a USERS table, structed like this:</p> <pre><code>CREATE TABLE IF NOT EXISTS `users` ( `id` int(11) NOT NULL AUTO_INCREMENT, `username` varchar(255) COLLATE utf8_turkish_ci NOT NULL, PRIMARY KEY (`id`), KEY `username` (`username`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_turkish_ci AUTO_INCREMENT=9422 ; </code></pre> <p>I'm using this query to get latest "page, file or post" posts ordered by descending time and grouping by user to not show all latest posts from a user:</p> <pre><code> SELECT p.*, u.* FROM posts p LEFT JOIN users u ON p.user_id = u.id WHERE p.type IN ('post', 'page', 'file') GROUP BY p.user_id ORDER BY p.created_at DESC LIMIT 30 </code></pre> <p>But it is too slow, even limited to 30 records.</p> <p>now, how can i speed up this query? which columns to index or any other ideas? thanks.</p>
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