sql怎样连接join（一张图看懂SQL的各种）

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

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