mysql - 私のクエリは、結合すると非常に遅くなりますが、個別には高速です

Question

私の両方のクエリは別々に高速に動作しますが、両方のクエリを結合すると実行に時間がかかります。

SELECT b.*, 
       a.* 
FROM   (SELECT r.vou_no, 
               r.vou_date, 
               r.lr_date, 
               r.due_date, 
               r.vac_code, 
               r.vamount, 
               r.vmfg_amt, 
               r.vter_cd, 
               r.mkt_year, 
               r.mnth_code 
        FROM   ledfile AS r 
        WHERE  r.mkt_year = 2012 
               AND r.mnth_code BETWEEN 201210 AND 201306 
               AND r.div_code = 1 
               AND r.vdepo_code = 21 
               AND r.vbook_cd = 80 
               AND Ifnull(r.del_tag, '') <> 'D' 
        ORDER  BY r.vac_code, 
                  r.vou_date, 
                  r.vou_no) b, 
       (SELECT a.vac_code vcode, 
               a.vouno, 
               a.bill_date, 
               a.vamount  vamt, 
               a.vou_date vdate 
        FROM   rcpfile a 
        WHERE  a.mkt_year = 2012 
               AND a.div_code = 1 
               AND a.vdepo_code = 21 
               AND a.vbook_cd IN ( 20, 21, 22, 90, 
                                   98, 80 ) 
               AND Ifnull(a.del_tag, '') <> 'D' 
        ORDER  BY a.vac_code, 
                  a.bill_date, 
                  a.vouno) a 
WHERE  a.vcode = b.vac_code 
       AND a.vouno = b.vou_no 
       AND a.bill_date = b.vou_date;