左连接、右连接、内连接、外连接，通过一张图片了解 SQL 7 JOIN 的用法

与 LEFT JOIN、RIGHT JOIN、INNER JOIN、OUTER JOIN 相关的 7 个用法。

具体细分如下：

1.INNER JOIN（内连接）

SELECT <select_list> 
FROM Table_A A
INNER JOIN Table_B B
ON A.Key = B.Key

2.LEFT JOIN（左连接）

SELECT <select_list>
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key

3.RIGHT JOIN（右连接）

SELECT <select_list>
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key

4.OUTER JOIN （外连接） )

SELECT <select_list>
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.Key = B.Key

5.LEFT JOIN EXCLUSIVE INNER JOIN（左连接-内连接）

SELECT <select_list> 
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key
WHERE B.Key IS NULL

6.RIGHT JOIN EXCLUSIVE INNER JOIN（右连接-内连接）

SELECT <select_list>
FROM Table_A A
RIGHT JOIN Table_B B
ON A.Key = B.Key
WHERE A.Key IS NULL

7.OUTER JOIN EXCLUSIVE INNER JOIN (外连接）-内连接）连接）

SELECT <select_list>
FROM Table_A A
FULL OUTER JOIN Table_B B
ON A.Key = B.Key
WHERE A.Key IS NULL OR B.Key IS NULL