mysql> DESC ftransrembt;
+----------------------+-----------+------+-----+-------------------+-----------------------------+
| Field                | Type      | Null | Key | Default           | Extra                       |
+----------------------+-----------+------+-----+-------------------+-----------------------------+
| trnumremboursement_l | int(11)   | NO   | PRI | 0                 |                             |
| trnumorigine_l       | int(11)   | NO   | PRI | 0                 |                             |
| trmont_l             | int(11)   | YES  |     | NULL              |                             |
| trdatemodif_ts       | timestamp | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+----------------------+-----------+------+-----+-------------------+-----------------------------+
4 rows in set (0.00 sec)

mysql> SHOW CREATE TABLE  ftransrembt;
+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table       | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| ftransrembt | CREATE TABLE `ftransrembt` (
 `trnumremboursement_l` int(11) NOT NULL DEFAULT '0',
 `trnumorigine_l` int(11) NOT NULL DEFAULT '0',
 `trmont_l` int(11) DEFAULT NULL COMMENT 'Montant du remboursement',
 `trdatemodif_ts` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT 'Date et heure de derniere modification de l enregistrement',
 PRIMARY KEY (`trnumremboursement_l`,`trnumorigine_l`),
 KEY `trnumorigine_idx` (`trnumorigine_l`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> EXPLAIN SELECT 'toto',  (SELECT  CONCAT(SUM(ft.trmont_l),  count(*))   FROM ftrans AS ft INNER JOIN ftransrembt ON trnum_l = trnumremboursement_l WHERE trnumorigine_l = ftrans.trnum_l OR trnumremboursement_l = ftrans.trnum_l) AS total   FROM ftrans  WHERE trnum_l IN (113729282);+----+--------------------+-------------+-------------+--------------------------+--------------------------+---------+-------------------------------------------+------+----------------------------------------------------+
| id | select_type        | table       | type        | possible_keys            | key                      | key_len | ref                                       | rows | Extra                                              |
+----+--------------------+-------------+-------------+--------------------------+--------------------------+---------+-------------------------------------------+------+----------------------------------------------------+
|  1 | PRIMARY            | ftrans      | const       | PRIMARY                  | PRIMARY                  | 4       | const                                     |    1 | Using index                                        |
|  2 | DEPENDENT SUBQUERY | ftransrembt | index_merge | PRIMARY,trnumorigine_idx | trnumorigine_idx,PRIMARY | 4,4     | NULL                                      |    3 | Using union(trnumorigine_idx,PRIMARY); Using where |
|  2 | DEPENDENT SUBQUERY | ft          | eq_ref      | PRIMARY                  | PRIMARY                  | 4       | tpewebv2.ftransrembt.trnumremboursement_l |    1 |                                                    |
+----+--------------------+-------------+-------------+--------------------------+--------------------------+---------+-------------------------------------------+------+----------------------------------------------------+
3 rows in set (0.00 sec)

mysql> EXPLAIN SELECT 'toto',  (SELECT  CONCAT(SUM(ft.trmont_l),  count(*))   FROM ftrans AS ft INNER JOIN ftransrembt ON trnum_l = trnumremboursement_l WHERE trnumorigine_l = ftrans.trnum_l OR trnumremboursement_l = ftrans.trnum_l) AS total   FROM ftrans  WHERE trnum_l IN (113729282,317846840);
+----+--------------------+-------------+--------+--------------------------+------------------+---------+-------------------------------------------+--------+--------------------------+
| id | select_type        | table       | type   | possible_keys            | key              | key_len | ref                                        | rows   | Extra                    |
+----+--------------------+-------------+--------+--------------------------+------------------+---------+-------------------------------------------+--------+--------------------------+
|  1 | PRIMARY            | ftrans      | range  | PRIMARY                  | PRIMARY          | 4       | NULL                                      |      2 | Using where; Using index |
|  2 | DEPENDENT SUBQUERY | ftransrembt | index  | PRIMARY,trnumorigine_idx | trnumorigine_idx | 4       | NULL                                      | 198455 | Using where; Using index |
|  2 | DEPENDENT SUBQUERY | ft          | eq_ref | PRIMARY                  | PRIMARY          | 4       | tpewebv2.ftransrembt.trnumremboursement_l |      1 | Using where              |
+----+--------------------+-------------+--------+--------------------------+------------------+---------+-------------------------------------------+--------+--------------------------+
3 rows in set (0.00 sec)