MySQL的比較兩個表中查找匹配的記錄

Question

我試圖從tbl_attn_temp獲取所有數據，TraineeID是匹配tbl_assignedTraineeID或tbl_instructor_infoInstructorID。但我得到的所有數據與tbl_assignedTraineeID匹配。 tbl_instructor_info數據不或與此查詢，如下表示：

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

Your OR condition is wrong。它應該是這樣的WHERE（t1.TraineeID = t3.TraineeID OR t1.TraineeID = t2.InstructorID） 查詢應該是這樣的：

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

嘗試此查詢

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，則可以允許按列選擇組（traineeid，attnDate），並允許在一列或多列上執行集合函數。