一张图看懂 SQL 的各种 join 用法

作者：C.L. Moffatt http://www.codeproject.com/Articles/33052/Visual-Representation-of-SQL-Joins

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