INNER JOIN 与 IN

SELECT * FROM TMain;

 

SELECT * FROM TDetail;

 

 

SELECT a.*
FROM TMain a 
INNER JOIN TDetail b ON b.PID=a.ID;

  

SELECT * FROM TMain
WHERE ID IN (SELECT PID FROM TDetail);

 

 

总结：

当 INNER JOIN 关联的字段非唯一值时，会产生重复数据。

  

 

SELECT a.* FROM TMain a
WHERE EXISTS(SELECT PID FROM TDetail);

 

SELECT a.* FROM TMain a
WHERE EXISTS(SELECT PID FROM TDetail WHERE PID=a.ID);