Join的7中情况

一、左外连接

　　SELECT * FROM A LEFT JOIN B ON A.KEY = B.KEY

　　

二、右外连接　

　　SELECT * FROM A RIGHT JOIN B ON A.KEY = B.KEY

　　

三、内连接　

　　SELECT * FROM A INNER JOIN B ON A.KEY = B.KEY

　　

四、全连接　

1　　SELECT * FROM A FULL OUTER JOIN B ON A.KEY = B.KEY #Mysql不支持

　　

2　　SELECT * FROM A LEFT JOIN B ON A.KEY=B.KEY
　　 UNION
　　 SELECT * FROM A RIGHT JOIN B ON A.KEY=B.KEY

五、左连接

　　SELECT * FROM A LEFT JOIN B ON A.KEY = B.KEY WHERE B.KEY IS NULL

 　　

六、右连接

　　SELECT * FROM A RIGHT JOIN B ON A.KEY = B.KEY WHERE A.KEY IS NULL

 　　

七、全外连接

　1　SELECT * FROM A FULL OUTER JOIN B ON A.KEY = B.KEY WHERE A.KEY IS NULL OR B.KEY IS NULL #mysql不支持

 　　

　　

2　　SELECT * FROM A LEFT JOIN B ON A.KEY=B.KEY WHERE B.KEY IS NULL
　　　UNION
　　 SELECT * FROM A RIGHT JOIN B ON A.KEY=B.KEY WHERE A.KEY IS NULL