Mysql 5.7嵌套选择查询在抛出错误时
Unknown column 'CRoute.ID' in 'where clause'
这是我的查询
SELECT CTrip.ID, CRoute.Name,
(SELECT COUNT(StudentID) FROM CRouteStudent WHERE CRoute.ID = CRouteStudent.RouteID) AS ExpectedStudents,
(SELECT COUNT(*) FROM (SELECT COUNT(*) FROM CRouteStudent WHERE CRoute.ID = CRouteStudent.RouteID GROUP BY Stop) as a) AS ExpectedStops
FROM `CTrip`
JOIN `CRoute` ON `CRoute`.`ID` = `CTrip`.`RouteID`
JOIN `CRouteSchedule` ON `CRouteSchedule`.`RouteID`=`CTrip`.`RouteID`
WHERE `CTrip`.`Direction` = '1'
LIMIT 30
ExpectedStudents正在工作,ExpectedStops抛出错误
注意此查询在mysql 8.0中工作
答案 0 :(得分:0)
子查询嵌套得很深。
您可以尝试替换
(SELECT COUNT(*) FROM (SELECT COUNT(*) FROM CRouteStudent WHERE CRoute.ID = CRouteStudent.RouteID GROUP BY Stop) as a)
具有:
(SELECT count(DISTINCT stop)
FROM croutestudent
WHERE croute.id = croutestudent.routeid)
+
EXISTS (SELECT *
FROM croutestudent
WHERE croute.id = croutestudent.routeid
AND stop IS NULL)
如果+ EXISTS ...
不可为空,则可以将stop
部分保留。