mysql - SQL查询 - 查找不存在子帖子的父帖子

Question

我正在使用以下查询：

SELECT 
count(tblReplies.repDate) as comReplies,
tblReplies.repDate
FROM tblReplies, tblQuestions, tblUsers
WHERE
tblQuestions.queID = tblReplies.repQuestionID 
AND tblQuestions.queCompanyID = tblUsers.uCompanyID
AND tblUsers.uID = tblReplies.repUserID 
AND tblUsers.uCompanyID = $comID 
AND tblQuestions.queID = $queID 
GROUP BY tblReplies.repID 
ORDER BY tblReplies.repDate ASC

现在，我正在尝试修改查询以查找 tblQuestions (queID) 中没有回复的帖子（数据库 tblReplies 中没有子项的问题）。任何人都有一个想法，我完全迷路了，希望那里有一个忍者:)

谢谢，

Answer 1

select q.*
from tblQuestions q 
left outer join tblReplies r on q.queID = r.repQuestionID
where r.repQuestionID is null

Answer 2

使用NOT EXISTS：

SELECT q.* 
FROM   tblquestions q
WHERE  NOT EXISTS (SELECT 1 
                   FROM   tblreplies r
                   WHERE  r.repquestionid = q.queid)