我正在运行一个mysql 数据库。我有两个表，分别存储对帖子的点赞和评论。
点赞表:
+--------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| post_id | int(11) | NO | | NULL | |
| user_id | varchar(255) | NO | | NULL | |
| created_at | timestamp | YES | | NULL | |
| updated_at | timestamp | YES | | NULL | |
+--------------+------------------+------+-----+---------+----------------+
评论表:
+--------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| post_id | int(11) | NO | | NULL | |
| user_id | varchar(255) | NO | | NULL | |
| comment | varchar(255) | NO | | NULL | |
| created_at | timestamp | YES | | NULL | |
| updated_at | timestamp | YES | | NULL | |
+--------------+------------------+------+-----+---------+----------------+
我需要获取唯一的用户 ID 以及他们的点赞数和评论数。
我运行了以下查询:
select * from
(select user_id, count(*) as like_count from post_likes group by user_id) as a,
(select user_id, count(*) as comment_count from post_comments group by user_id) as b
limit 5
查询 180 万条记录(两个表的总和)耗时 66 秒。此外，它没有给出正确的结果。
如果我执行 LEFT JOIN，它只返回左表中的匹配记录，而我需要从两个表中返回，即如果用户 ID 只喜欢但没有评论或只评论但不喜欢。
我想得到的是这样的:
+--------------+------------------+------+-----+---------+
| user_id | like_count | comment_count |
+--------------+------------------+------+-----+---------+
| 1 | 1213 | 310 |
| 2 | 1098 | 0 |
| 3 | 0 | 115 |
+--------------+------------------+------+-----+---------+
最佳答案
理想的方法是在用户表上LEFT JOIN，例如:
SELECT u.user_id, COUNT(l.id), COUNT(c.id)
FROM users u LEFT JOIN Likes l ON u.user_id = l.user_id
LEFT JOIN Comments c ON u.user_id = c.user_id;
关于mysql - 从两个表中查找唯一 ID 并从两个表中查找相应的计数，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/44278730/