一张图看懂 SQL 的各种 join 用法！

一张图看懂 SQL 的各种 join 用法！

SQL中的JOIN操作是数据查询中非常重要的一个环节，它允许我们从多个表中获取数据。本文通过一张图和详细的代码示例，帮助读者快速掌握7种常见的JOIN用法。

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

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