SQL 的各种 join 用法

下图展示了 LEFT JOIN、RIGHT JOIN、INNER JOIN、OUTER JOIN 相关的 7 种用法。

具体分解如下：

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 EXCLUDING 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 EXCLUDING 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 EXCLUDING INNER JOIN（外连接-内连接）

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