两个查询的比较（MySQL）

我有两个问题。它们相同吗

DELETE FROM t1 
USING t1 
LEFT JOIN t2 using(key) 
WHERE t2.key is null

DELETE t1 
FROM t1  
LEFT JOIN t2 using(key) 
WHERE t2.key is null

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如果是，哪一个更有效？

在我看来，这两个语法都是相同的：

DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM tbl_name
    [WHERE where_condition]
    [ORDER BY ...]
    [LIMIT row_count]

多表语法：

DELETE [LOW_PRIORITY] [QUICK] [IGNORE]
    tbl_name[.*] [, tbl_name[.*]] ...
    FROM table_references
    [WHERE where_condition]

或：

至于关注哪一个更有效？这取决于我们在何时何地使用它的情况

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阅读此文以获得更好的体验：

第一条看起来无效。没有连接就不能使用。

DELETE [LOW_PRIORITY] [QUICK] [IGNORE]
    FROM tbl_name[.*] [, tbl_name[.*]] ...
    USING table_references
    [WHERE where_condition]