MariaDB [federated]> explain DELETE FROM `OUTR1` USING (
    -> 
    ->   (
    -> 
    ->     `federated`.`B` `OUTR2`
    -> 
    ->     JOIN `federated`.`D` `OUTR3` 
    -> 
    ->       ON (`federated`.`OUTR2`.`pk` > `federated`.`OUTR3`.`col_int_key`)
    -> 
    ->   )
    -> 
    ->   LEFT JOIN `federated`.`D` `OUTR1` 
    -> 
    ->     ON (`federated`.`OUTR1`.`col_int_nokey` = `federated`.`OUTR2`.`col_int_key`)
    -> 
    -> )
    -> 
    -> WHERE 
    -> 
    ->   `federated`.`OUTR1`.`col_int_key` IN (
    -> 
    ->     SELECT 
    -> 
    ->       `federated`.`INNR1`.`pk`
    -> 
    ->     FROM 
    -> 
    ->       `federated`.`CC` `INNR1`
    -> 
    ->     WHERE 
    -> 
    ->       `federated`.`INNR1`.`col_int_nokey` <= 1 
    -> 
    ->       OR `federated`.`INNR1`.`pk` <= 4
    -> 
    ->     
    -> 
    ->     UNION
    -> 
    ->     
    -> 
    ->     SELECT 
    -> 
    ->       `federated`.`INNR1`.`pk`
    -> 
    ->     FROM 
    -> 
    ->       `federated`.`AA` `INNR1`
    -> 
    ->     GROUP BY 
    -> 
    ->       `federated`.`INNR1`.`col_int_uniq`
    -> 
    ->     HAVING 
    -> 
    ->       COUNT(0) >= 2
    -> 
    ->   );
+------+--------------------+------------+--------+---------------+---------+---------+------+------+------------------------------------------------+
| id   | select_type        | table      | type   | possible_keys | key     | key_len | ref  | rows | Extra                                          |
+------+--------------------+------------+--------+---------------+---------+---------+------+------+------------------------------------------------+
|    1 | PRIMARY            | OUTR2      | index  | PRIMARY       | k_int   | 5       | NULL | 100  | Using index                                    |
|    1 | PRIMARY            | OUTR3      | ALL    | k_int         | NULL    | NULL    | NULL | 100  | Range checked for each record (index map: 0x4) |
|    1 | PRIMARY            | OUTR1      | ALL    | NULL          | NULL    | NULL    | NULL | 100  | Using where                                    |
|    2 | DEPENDENT SUBQUERY | INNR1      | eq_ref | PRIMARY       | PRIMARY | 4       | func | 1    | Using where                                    |
|    3 | DEPENDENT UNION    | INNR1      | index  | NULL          | u_int   | 5       | NULL | 1    | Using index                                    |
| NULL | UNION RESULT       | <union2,3> | ALL    | NULL          | NULL    | NULL    | NULL | NULL |                                                |
+------+--------------------+------------+--------+---------------+---------+---------+------+------+------------------------------------------------+
6 rows in set (0.001 sec)

MariaDB [federated]> notee