mysql比较两个表来查找匹配的记录

Question

我正在尝试从tbl_attn_temp获取TraineeID与tbl_assigned TraineeID或tbl_instructor_info InstructorID匹配的所有数据。但我将所有数据与tbl_assigned TraineeID匹配。 tbl_instructor_info数据未显示或显示此查询，如下所示：

tbl_attn_temp

tbl_assigned

tbl_instructor_info

SELECT t1.*
FROM tbl_attn_temp t1, tbl_instructor_info t2, tbl_assigned t3
WHERE t1.TraineeID=t3.TraineeID or t2.InstructorID
GROUP by t1.traineeid, t1.attnDate

Answer 1

您的OR条件错误。它应该是这样的 WHERE（t1.TraineeID = t3.TraineeID或t1.TraineeID = t2.InstructorID） 查询应该是这样的：

SELECT t1.*
FROM tbl_attn_temp t1, tbl_instructor_info t2, tbl_assigned t3
WHERE (t1.TraineeID = t3.TraineeID OR t1.TraineeID = t2.InstructorID)
GROUP by t1.traineeid, t1.attnDate

Answer 2

尝试此查询

SELECT t1.traineeid, t1.attnDate
FROM tbl_attn_temp t1, tbl_instructor_info t2, tbl_assigned t3
WHERE (t1.TraineeID=t3.TraineeID or t1.TraineeID=t2.InstructorID)
GROUP by t1.traineeid, t1.attnDate

如果使用GROUP BY子句，则可以允许按列选择（在您的情况下为traineeid，attnDate），并允许在一列或多列上执行聚合函数。