我有 MySQL 数据库,其中有 3 个表,如下所示
表:subject_master
-----------------------
subjectId | subjectName
--------------------------------------
1 | English
2 | German
3 | French
4 | Spanish
表:class_Master
----------------------------------
classId | className
---------------------------------------
1 | Alpha
2 | Beta
3 | Gama
4 | laser
表:subjectAllocation
-------------------------------------------------------
allocationId | classId | subjectId
------------------------------------------------------
1 | 1(Alpha) | 1,2,3
2 | 2 (Beta) | 2,3
3 | 4 (laser) | 4,2,1
如何获取每个主题的类名列表
subjectName | classNames
-------------------------------------
English | Alpha, laser
German | Alpha, Beta, laser
French | Beta,Gama
Spanish | laser
我学习了 GROUP_CONCAT 和 FIND_IN_SET 但无法一起使用,如下所示
SELECT
a.subjectName, FIND_IN_SET(c.className , (GROUP_CONCAT(b.classId))
FROM
subject_master a
LEFT JOIN subjectAllocation b ON a.subjectId = b.sectionId
LEFT JOIN class_master c ON b.classId = c.classId
GROUP BY a.subjectId
最佳答案
您应该在 ON
子句中使用 FIND_IN_SET
来匹配列表中的元素,而不是在 SELECT
子句中。
SELECT a.subjectName, GROUP_CONCAT(c.className) AS classNames
FROM subject_master AS a
LEFT JOIN subjectAllocation AS b ON FIND_IN_SET(a.subjectId, b.subjectId)
LEFT JOIN class_Master AS c ON b.classId = c.classId
GROUP BY a.subjectId
关于MySQL 一起使用 GROUP CONCAT 和 FIND_IN_SET,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/34682534/