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

这可能是因为它pID是暧昧的Professor而且没有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 = ?;