php – Mysql如何从同一个表中的单个查询中获取2组结果？

我有这样的 mysql 评论表.

+------------+------------------+------+-----+---------+----------------+
| Field      | Type             | Null | Key | Default | Extra          |
+------------+------------------+------+-----+---------+----------------+
| userid     | int(11)          | NO   |     | 0       |                |
| comment    | char(255)        | NO   |     | NULL    |                |
| content    | int(11)          | NO   | MUL | 0       |                |
| ratings    | int(11)          | NO   |     | 0       |                |
| datetime   | datetime         | NO   |     | NULL    |                |
| ip         | int(10) unsigned | NO   |     | NULL    |                |
| is_updated | tinyint(2)       | NO   |     | 0       |                |
| record_num | int(11)          | NO   | PRI | NULL    | auto_increment |
+------------+------------------+------+-----+---------+----------------+

现在我可以使用像这样的INNER JOIN查询从另一个表中获取来自此用户名和用户名的注释.

我可以获得前3条评论ORDER BY comments.ratings DESC

SELECT comments.userid,users.username,comments.comment,comments.ratings,comments.datetime,comments.record_num,content.uploader,content.anonymous
FROM comments 
LEFT JOIN users ON  comments.userid = users.record_num 
LEFT JOIN content ON comments.content = content.record_num
WHERE comments.content = ? ORDER BY comments.ratings DESC limit 3

和

获得定期评论ORDER BY comments.datetime DESC.

SELECT comments.userid,content.anonymous
FROM comments 
LEFT JOIN users ON  comments.userid = users.record_num 
LEFT JOIN content ON comments.content = content.record_num
WHERE comments.content = ? ORDER BY comments.datetime DESC limit ?,?

我正在尝试做的是首先通过评级向用户显示前3条评论,然后通过comments.datetime DESC定期评论.

现在我怎么能将上面两个mySQL查询加入到一个？

正如另一个答案所说 – 你可以使用union来组合结果 – 这只是意味着将两个结果连接在一起.但是,重要的是要注意,你不能简单地将这两个查询直接组合在一起,因为它们使用order by,所以我们需要将它们包装在外部查询中,并使用排名变量来确保我们可以重建联合按照我们想要的顺序：

select * from (
    SELECT 1 as tbl,comments.userid,content.anonymous,@rank := @rank + 1 as rank
    FROM comments 
      LEFT JOIN users ON  comments.userid = users.record_num 
      LEFT JOIN content ON comments.content = content.record_num
      CROSS JOIN (select @rank := 0 ) q
    WHERE comments.content = ? ORDER BY comments.ratings DESC limit 3
) q1    
UNION ALL
select * from (    
    SELECT 2 as tbl,@rank := @rank + 1 as rank
    FROM comments 
      LEFT JOIN users ON  comments.userid = users.record_num 
      LEFT JOIN content ON comments.content = content.record_num
      CROSS JOIN (select @rank := 0 ) q
    WHERE comments.content = ? ORDER BY comments.datetime DESC limit ?,?
) q2
ORDER BY tbl asc,rank asc;

默认情况下,union是不同的意思,它不会复制在两个结果集中找到的行,但是也不能保证按照您期望的顺序返回行,因此需要使用自己的tbl值标记每个表,然后按该字段排序.

如果您确定不存在重复项,则可以使用union all而不是union来消除重复检查

原文链接：https://www.f2er.com/php/137704.html

php – Mysql如何从同一个表中的单个查询中获取2组结果？

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