MySQL中条件放在where后面与放在on后面的区别

* FROM test_on_position LEFT JOIN address ON test_on_position.address = address.id WHERE test_on_position.address IS NOT NULL

运行结果：

条件在on后面

 SELECT
     * 
FROM
    test_on_position
LEFT JOIN address ON test_on_position.address  = address.id AND test_on_position.address IS NOT NULL

运行结果：

结果分析

当条件放在on后面时，无论on条件的真假，都会返回左表的值；

当条件放在where后面时，只有满足条件的记录会返回。

inner join

条件在on后面

 SELECT
     * 
FROM
    test_on_position
INNER JOIN address ON test_on_position.address  = address.id AND test_on_position.address IS NOT NULL

运行结果：

条件在where后面

 SELECT
     * 
FROM
    test_on_position
INNER JOIN address ON test_on_position.address  =  address.id
WHERE
    test_on_position.address IS NOT NULL 

运行结果：

结果分析

无论条件放在哪里，都只会返回满足条件的结果。

MySQL中条件放在where后面与放在on后面的区别

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