三个表联合sql语句，查不出来num,一直为0，真心求教！！

Question

三个表联合sql语句，查不出来num,sql语句：select u.UserName,ISNULL (t.num,0) num,l.* from Logs l left join (select LogID,count(CommentID) num from Comments where CommentID is null group by logId ) t on l.LogID =t.logID left join Users u on l.userID=u.UserID where l.LogStatus=1

Answer 1

mysql join语法 http://www.data.5helpyou.com/article209.html