mysql - MySQL 子句上的未知列

Question

第一个查询有效：

SELECT video.seller from video;

第二个不是：

SELECT SQL_CALC_FOUND_ROWS *,
       t.name as tname
FROM video, type as t 
INNER JOIN user 
ON video.seller = user.id 
WHERE video.type2 = t.id 
AND thumbnail_blobKey != '' 
AND disabled = 0 
AND is_reel = 0 
AND price!= 0 
AND video.type != 4  
GROUP BY video.id 
ORDER BY video.id DESC LIMIT 0, 10

错误：“on 条款”中的未知列“video.seller”

Answer 1

这是一个有趣的例子。更好的格式：

SELECT SQL_CALC_FOUND_ROWS *, t.name as tname
FROM video, type as t INNER JOIN
     user
     ON video.seller = user.id
WHERE video.type2 = t.id AND
     thumbnail_blobKey != '' AND disabled = 0 AND is_reel = 0 AND price!= 0 AND video.type != 4 
GROUP BY video.id
ORDER BY video.id DESC
LIMIT 0, 10

问题video是from由于,. 这就是逗号的工作原理。有趣的是，它可以通过,用它的逻辑等价替换来修复cross join：

SELECT SQL_CALC_FOUND_ROWS *, t.name as tname
FROM video cross join type as t INNER JOIN
     user
     ON video.seller = user.id
WHERE video.type2 = t.id AND
     thumbnail_blobKey != '' AND disabled = 0 AND is_reel = 0 AND price!= 0 AND video.type != 4 
GROUP BY video.id
ORDER BY video.id DESC
LIMIT 0, 10

这在文档中进行了解释，原因是优先级。逗号的优先级低于cross join。因此，表达式中的连接被评估为“视频连接（类型连接用户）”。因为第二个连接首先被解释，所以其中的列video是未知的。

但是，表上确实有一个join，所以最好写成：

SELECT SQL_CALC_FOUND_ROWS *, t.name as tname
FROM video join
     type t
     on video.type2 = t.id INNER JOIN
     user
     ON video.seller = user.id
WHERE thumbnail_blobKey != '' AND disabled = 0 AND is_reel = 0 AND price!= 0 AND video.type != 4 
GROUP BY video.id
ORDER BY video.id DESC
LIMIT 0, 10

Answer 2

正如现在所写的那样，您正在尝试连接表type，并且user有条件video.seller = user.id。由于 video.seller 既不是表格的一列，type也不是user，您有一个错误。

更改为以下内容将消除此错误：

    SELECT SQL_CALC_FOUND_ROWS *,
       t.name AS tname
FROM video
INNER JOIN USER ON video.seller = USER.id,
                                       TYPE AS t
WHERE video.type2 = t.id
  AND thumbnail_blobKey != ''
  AND disabled = 0
  AND is_reel = 0
  AND price!= 0
  AND video.TYPE != 4
GROUP BY video.id
ORDER BY video.id DESC LIMIT 0,
                             10