mysql> EXPLAIN  (SELECT  `join_1_0`.`col39`,  `join_1_0`.`col39`,  `join_1_0`.`col39`,  `join_1_0`.`col39`,  `join_0_0`.`col22`,  `join_0_0`.`col22`,  `join_0_0`.`col22`,  `join_0_0`.`col22`  FROM `table76` AS `join_0_0`, `table335` AS `join_1_0`  WHERE `join_0_0`.`col22`=`join_1_0`.`col39`  OR `join_0_0`.`col29`='?'  AND `join_1_0`.`col113`='?'   GROUP BY `join_1_0`.`col39`,`join_0_0`.`col22`  ORDER BY  NULL )  UNION  (SELECT  `join_0_1`.`col1`,  `join_1_1`.`col38`,  `join_1_1`.`col38`,  `join_1_1`.`col38`,  `join_0_1`.`col1`,  `join_1_1`.`col38`,  `join_0_1`.`col1`,  `join_0_1`.`col1`  FROM `table267` AS `join_0_1`, `table229` AS `join_1_1`  WHERE `join_0_1`.`col1`=`join_1_1`.`col38`  OR `join_0_1`.`col1`='?'  OR `join_1_1`.`col32`='?'   GROUP BY `join_1_1`.`col38`,`join_1_1`.`col38`,`join_1_1`.`col38`,`join_1_1`.`col38`,`join_1_1`.`col38`,`join_0_1`.`col1`,`join_1_1`.`col38`,`join_0_1`.`col1`,`join_0_1`.`col1`  ORDER BY `join_1_1`.`col38` ASC,`join_0_1`.`col1` ASC,`join_1_1`.`col38` ASC,`join_0_1`.`col1` DESC,`join_1_1`.`col38` ASC,`join_1_1`.`col38` ASC)  UNION  (SELECT  `join_0_2`.`col24`,  `join_1_2`.`col23`,  `join_1_2`.`col23`,  `join_0_2`.`col24`,  `join_0_2`.`col24`,  `join_0_2`.`col24`,  `join_0_2`.`col24`,  `join_0_2`.`col24`  FROM `table76` AS `join_0_2`, `table859` AS `join_1_2`  WHERE `join_0_2`.`col24`=`join_1_2`.`col23`  XOR `join_0_2`.`col20`='?'  AND `join_1_2`.`col0`='?'   GROUP BY `join_1_2`.`col23`,`join_1_2`.`col23`,`join_1_2`.`col23`  ORDER BY `join_1_
2`.`col23` ASC) \G
*************************** 1. row ***************************
           id: 1
  select_type: PRIMARY
        table: join_1_0
         type: ALL
possible_keys: idx1,idx2
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 22
        Extra: Using temporary; Using filesort
*************************** 2. row ***************************
           id: 1
  select_type: PRIMARY
        table: join_0_0
         type: ALL
possible_keys: idx1,idx7,idx10,idx35,idx39
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 33
        Extra: Range checked for each record (index map: 0x8800000482)
*************************** 3. row ***************************
           id: 2
  select_type: UNION
        table: join_0_1
         type: index
possible_keys: idx0,idx2,idx4,idx6,idx8,idx10,idx11,idx12
          key: idx8
      key_len: 3
          ref: NULL
         rows: 10
        Extra: Using index; Using temporary; Using filesort; Using join cache
*************************** 4. row ***************************
           id: 2
  select_type: UNION
        table: join_1_1
         type: ALL
possible_keys: idx1,idx3
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 25
        Extra: Using where
*************************** 5. row ***************************
           id: 3
  select_type: UNION
        table: join_0_2
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 33
        Extra: Using temporary; Using filesort; Using join cache
*************************** 6. row ***************************
           id: 3
  select_type: UNION
        table: join_1_2
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 37
        Extra: Using where
*************************** 7. row ***************************
           id: NULL
  select_type: UNION RESULT
        table: <union1,2,3>
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: NULL
        Extra:
7 rows in set, 2 warnings (1.67 sec)

mysql> show warnings;
+---------+------+-----------------------------------------------------------+
| Level   | Code | Message                                                   |
+---------+------+-----------------------------------------------------------+
| Warning | 1292 | Incorrect datetime value: '?' for column 'col32' at row 1 |
| Warning | 1292 | Incorrect datetime value: '?' for column 'col32' at row 1 |
+---------+------+-----------------------------------------------------------+
2 rows in set (0.02 sec)