SQL WHERE IN处理SELECT语句需要很长时间

Question

我想重构下面的查询，因为它需要一些时间来处理:

SELECT `user_product`.* FROM `user_products` AS `user_product`
INNER JOIN `items` ON (`user_product`.`item_id` = `items`.`id`) 
INNER JOIN `user_tags` ON (`items`.`id` = `user_tags`.`item_id`)
INNER JOIN `tags` ON (`user_tags`.`tag_id` = `tags`.`id`)
WHERE `tags`.`title` IN ('tag3', 'tag')
GROUP BY `items`.`id`
ORDER BY `items`.`created_at` DESC

当我执行EXPLAIN时，我得到以下结果:

+----+-------------+--------------+--------+---------------+---------+---------+----------------------+-------+---------------------------------+
| id | select_type | table        | type   | possible_keys | key     | key_len | ref                  | rows  | Extra                           |
+----+-------------+--------------+--------+---------------+---------+---------+----------------------+-------+---------------------------------+
| 1  | SIMPLE      | user_tags    | ALL    | NULL          | user_id | 12      | NULL                 | 27802 | Using temporary; Using filesort |
| 1  | SIMPLE      | user_product | ALL    | NULL          | NULL    | NULL    | NULL                 | 22676 | Using where; Using join buffer  |
| 1  | SIMPLE      | items        | eq_ref | PRIMARY       | PRIMARY | 4       | user_product.item_id | 1     | Using where                     |
| 1  | SIMPLE      | tags         | eq_ref | PRIMARY,title | PRIMARY | 4       | user_tags.tag_id     | 1     | Using where                     |
+----+-------------+--------------+--------+---------------+---------+---------+----------------------+-------+---------------------------------+

查询用时17秒，WHERE IN中有两个标签，而0.009中有一个标签。优化查询的最佳方法是什么?

Answer 1

尝试在user_tags上添加索引。Item_id和user_products.item_id

Answer 2

MySQL应该在in语句中处理一组常量。您是否对每个标记的查询进行了独立计时?其中一个标签可能有很多数据。

如果你在tag .title.