Возможный намек:
mysql>
mysql> CREATE TABLE test (
-> id SMALLINT unsigned NOT NULL AUTO_INCREMENT PRIMARY KEY
-> ) ENGINE=InnoDB;
Query OK, 0 rows affected (0.02 sec)
mysql> INSERT INTO test () VALUES
-> (),(),(),(),(),(),(),(),(),(),
-> (),(),(),(),(),(),(),(),(),(),
-> (),(),(),(),(),(),(),(),(),();
Query OK, 30 rows affected (0.01 sec)
Records: 30 Duplicates: 0 Warnings: 0
mysql> DELETE FROM t USING
-> test t JOIN (
-> SELECT id
-> FROM (
-> SELECT id
-> FROM test
-> ORDER BY id DESC
-> LIMIT 20, 1000
-> ) as ids) as ids ON t.id = ids.id;
Query OK, 10 rows affected (0.01 sec)
mysql> SELECT * FROM test;
+----+
| id |
+----+
| 11 |
| 12 |
| 13 |
| 14 |
| 15 |
| 16 |
| 17 |
| 18 |
| 19 |
| 20 |
| 21 |
| 22 |
| 23 |
| 24 |
| 25 |
| 26 |
| 27 |
| 28 |
| 29 |
| 30 |
+----+
20 rows in set (0.00 sec)