What does the MySQL USING statement do in conjunction with DELETE?

What does the MySQL USING statement do and is 开发者_开发技巧there any docs on this?

MySQL USING statement example

DELETE FROM l, s 
USING l
INNER JOIN s ON s.skill_id = l.id
WHERE s.user_id = 3

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In a DELETE, you can list tables after the USING clause, from which rows do not get deleted (i.e., to only be part of the WHERE clause). For example:

DELETE FROM t1, t2 
  USING t1 
    INNER JOIN t2 
    INNER JOIN t3
  WHERE t1.id=t2.id AND 
        t2.id=t3.id;

Your particular example can be achieved without USING in this fashion:

DELETE l,s 
FROM l 
  INNER JOIN s 
    ON s.skill_id = l.id 
WHERE s.user_id = 3 

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The USING clause is used to set column existence criteria for two tables in a JOIN.

So, if I have a statement such as:

SELECT * from a
JOIN b
USING (c1,c2)
...

what will happen is that the MySQL engine will first verify that columns c1 and c2 exist in both tables, and then compare the values of those columns to perform the join on the two tables.

See MySQL documentation for JOIN Syntax.

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Search for USING in the MySQL documentation for DELETE. It is just an alternative syntax.

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Syntax for USING statement -

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

for detailed info visit USING