使用的 SELECT 语句具有不同的列数(REDUX ！！)

2021-11-20 00:00:00 sql mysql mysql-error-1222

还有一个与此类似的问题，但它似乎没有回答我的问题.

There's another question out there similar to this, but it didn't seem to answer my question.

我的问题是:为什么我会返回这个错误 ERROR 1222 (21000): The used SELECT statements have a different number of columns 来自以下 SQL

My question is this: why am I getting back this error ERROR 1222 (21000): The used SELECT statements have a different number of columns from the following SQL 

SELECT * FROM friends
LEFT JOIN users AS u1 ON users.uid = friends.fid1
LEFT JOIN users AS u2 ON users.uid = friends.fid2
WHERE (friends.fid1 = 1) AND (friends.fid2 > 1)
UNION SELECT fid2 FROM friends
WHERE (friends.fid2  = 1) AND (friends.fid1 < 1)
ORDER BY RAND()
LIMIT 6;

这是用户:

+------------+---------------+------+-----+---------+----------------+
| Field      | Type          | Null | Key | Default | Extra          |
+------------+---------------+------+-----+---------+----------------+
| uid        | int(11)       | NO   | PRI | NULL    | auto_increment |
| first_name | varchar(50)   | NO   |     | NULL    |                |
| last_name  | varchar(50)   | NO   |     | NULL    |                |
| email      | varchar(128)  | NO   | UNI | NULL    |                |
| mid        | varchar(40)   | NO   |     | NULL    |                |
| active     | enum('N','Y') | NO   |     | NULL    |                |
| password   | varchar(64)   | NO   |     | NULL    |                |
| sex        | enum('M','F') | YES  |     | NULL    |                |
| created    | datetime      | YES  |     | NULL    |                |
| last_login | datetime      | YES  |     | NULL    |                |
| pro        | enum('N','Y') | NO   |     | NULL    |                |
+------------+---------------+------+-----+---------+----------------+

这里是朋友:

+---------------+--------------------------------------+------+-----+---------+----------------+
| Field         | Type                                 | Null | Key | Default | Extra          |
+---------------+--------------------------------------+------+-----+---------+----------------+
| friendship_id | int(11)                              | NO   | MUL | NULL    | auto_increment |
| fid1          | int(11)                              | NO   | PRI | NULL    |                |
| fid2          | int(11)                              | NO   | PRI | NULL    |                |
| status        | enum('pending','accepted','ignored') | NO   |     | NULL    |                |
+---------------+--------------------------------------+------+-----+---------+----------------+

如果您也想对这里发生的任何疯狂事情提供任何反馈，请随时提出.我会吃我的肿块.

If you want to give any feedback on anything crazy you see going on here, as well, please feel free to do so. I'll take my lumps.

推荐答案

UNION(UNION 和 UNION ALL)要求所有被 UNION 连接的查询:

UNIONs (UNION and UNION ALL) require that all the queries being UNION'd have:

  1. SELECT 子句中的列数相同
  2. 列数据类型必须在每个位置匹配

您的查询有:

SELECT f.*, u1.*, u2.* ...
UNION 
SELECT fid2 FROM friends

我最简单的重写是:

   SELECT f.*, u.*
     FROM FRIENDS AS f
     JOIN USERS AS u ON u.uid = f.fid2
    WHERE f.fid1 = 1 
      AND f.fid2 > 1
UNION 
   SELECT f.*, u.*
     FROM FRIENDS AS f
     JOIN USERS AS u ON u.uid = f.fid1
    WHERE f.fid2  = 1 
      AND f.fid1 < 1
ORDER BY RAND()
LIMIT 6;

您已 LEFT JOIN 到 USERS 表两次，但似乎没有使用这些信息.

You've LEFT JOIN'd to the USERS table twice, but don't appear to be using the information.

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