Slow query on tmp table

[Eric Colson]

Hi all,

I Try to execute this query:

SELECT str_nom_magasin, e.Str_Code_Devise,
COUNT(ID_Ticket) AS nb_tickets,
SUM(Dbl_Montant_TTC_Rem) / (SELECT dbl_taux_conv_dev_pale from t_devise WHERE code_devise = e.Str_Code_Devise) AS ca_ttc,
SUM(DBL_Montant_Marge) / (SELECT dbl_taux_conv_dev_pale from t_devise WHERE code_devise = e.Str_Code_Devise) AS marge
FROM t_ent_ticket e
INNER JOIN t_magasin m ON m.id_magasin = e.id_magasin
WHERE str_dat_valid BETWEEN "20151109" AND "20151116"
AND e.int_est_annule = 0 AND e.int_est_attente = 0
GROUP BY 1, 2
ORDER BY 4 DESC;

Sometimes a few seconds are required, sometimes a lot of minuts.

Here's the EXPLAIN:
"id" "select_type" "table" "type" "possible_keys" "key" "key_len" "ref" "rows" "Extra"
"1" "PRIMARY" "m" "ALL" "PRIMARY" \N \N \N "16" "Using temporary; Using filesort"
"1" "PRIMARY" "e" "ref" "DATES,HEURES,id_magasin" "id_magasin" "4" "caisse.m.ID_Magasin" "3708" "Using where"
"3" "DEPENDENT SUBQUERY" "t_devise" "ref" "DEV1" "DEV1" "33" "func" "1" "Using where"
"2" "DEPENDENT SUBQUERY" "t_devise" "ref" "DEV1" "DEV1" "33" "func" "1" "Using where"

Thanks in advance if you can help me.