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

Question

What does the MySQL USING statement do and is 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

Answer 1

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