SQL Delete Rows Based on Another Table

Question

This is probably very easy, but it's Monday morning. I have two tables:

Table1:

Field        | Type             | Null | Key | Default | Extra
id           | int(32) unsigned | NO   | PRI | NULL    | auto_increment
group        | int(32)          | NO   |     | 0       |                

Table2:

Field     | Type             | Null | Key | Default | Extra
group     | int(32)          | NO   |     | 0       | 

Ignoring other fields...I would like a single SQL DELETE statement that will delete all rows in Table1 for which there exists a Table2.group equal to Table1.group. Thus, if a row of Table1 has group=69, that row should be deleted if and only if there exists a row in Table2 with group=69.

Thank you for any help.

Answer 1

I think this is what you want:

DELETE FROM `table1`
WHERE `group` in (SELECT DISTINCT `group` FROM `table2`)

Answer 2

I think this way is faster:

DELETE FROM t1 USING table1 t1 INNER JOIN table2 t2 ON ( t1.group = t2.group );

Answer 3

The nice solution is just writing the SQL as you say it yourself already:

DELETE FROM Table1
WHERE
  EXISTS(SELECT 1 FROM Table2 WHERE Table2.Group = Table1.Group)

Regards, Arno Brinkman