MySQL 三张图搞定连接（JOIN）

傷城~ 2021-10-19 01:54 225阅读 0赞

*  **INNER JOIN（内连接,或等值连接）**：获取两个表中字段匹配关系的记录。
 *  **JOIN（左连接）：**获取左表所有记录，即使右表没有对应匹配的记录。
 *  **RIGHT JOIN（右连接）：** 与 LEFT JOIN 相反，用于获取右表所有记录，即使左表没有对应匹配的记录。![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyMTgzNDA5_size_16_color_FFFFFF_t_70][]![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyMTgzNDA5_size_16_color_FFFFFF_t_70 1][]![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyMTgzNDA5_size_16_color_FFFFFF_t_70 2][]  
    基本语法：

INNER JOIN:

SELECT a.name , a.price ,b.name, b.price  FROM tmall a INNER  JOIN  jdong b ON a.id = b.id

这个内连接 相当于 WHERE语句的 SELECT a.name , a.price ,b.name, b.price  FROM tmall a ， jdong b WHERE a.id = b.id

LEFT  JOIN:

SELECT a.name , a.price ,b.name, b.price  FROM tmall a LEFT JOIN  jdong b ON a.id = b.id

RIGHT JOIN:

SELECT a.name , a.price ,b.name, b.price  FROM tmall a RIGHT JOIN  jdong b ON a.id = b.id

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