导语：一张图看懂 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：

1INNER JOIN（内连接）

SELECT <select_list> FROM Table_A AINNER JOIN Table_B BON A.Key = B.Key

2LEFT JOIN（左连接）

SELECT <select_list>FROM Table_A ALEFT JOIN Table_B BON A.Key = B.Key

3RIGHT JOIN（右连接）

SELECT <select_list>FROM Table_A ARIGHT JOIN Table_B BON A.Key = B.Key

4OUTER JOIN（外连接）

SELECT <select_list>FROM Table_A AFULL OUTER JOIN Table_B BON A.Key = B.Key

5LEFT JOIN EXCLUDING INNER JOIN（左连接-内连接）

SELECT <select_list> FROM Table_A ALEFT JOIN Table_B BON A.Key = B.KeyWHERE B.Key IS NULL

6RIGHT JOIN EXCLUDING INNER JOIN（右连接-内连接）

SELECT <select_list>FROM Table_A ARIGHT JOIN Table_B BON A.Key = B.KeyWHERE A.Key IS NULL

7OUTER JOIN EXCLUDING INNER JOIN（外连接-内连接）

SELECT <select_list>FROM Table_A AFULL OUTER JOIN Table_B BON A.Key = B.KeyWHERE A.Key IS NULL OR B.Key IS NULL

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