为什么这个SQL命令不起作用

Question

SELECT info, date
FROM Professor, Professor_Comment, Comment
WHERE pID = ?
AND Professor_Comment.pcID = Professor.pcID
AND Comment.commID = Professor_Comment.commID;
;

Answer 1

这可能是因为pID含糊不清而Professor没有pcID。

试试这个：

SELECT info, date
FROM Professor_Comment, Comment
WHERE pID = ?
AND Comment.commID = Professor_Comment.commID;

但是，我更喜欢显式的JOIN语法：

SELECT info, date
FROM Professor_Comment
JOIN Comment ON Comment.commID = Professor_Comment.commID
WHERE pID = ?;

Answer 2

1. 您有pID = ?，但pID不明确，因为它显示在Professor和Professor_Comment

   将唯一的pID更改为Professor.pID或Professor_Comment.pID
   
   

2. 您有Professor_Comment.pcID = Professor.pcID，教授表将其列为dID，而不是pcID