两个sql语句执行结果不一样???请教高手!!!!!!!
sql1、 select sum(a.fee)
FROM mid.mid_d_acct_charge a, mid.mid_d_user_flag b
WHERE a.acct_day = '20091018'
AND b.acct_day = '20091018'
AND a.user_no = b.user_no(+);
sql2、 select sum(a.fee)
FROM (select user_no,fee from mid.mid_d_acct_charge t where t.acct_day = '20091018') a,
(select user_no from mid.mid_d_user_flag t where t.acct_day = '20091018') b
WHERE a.user_no = b.user_no(+)
以上两个sql语句执行结果不一样,sql2的返回值比sql1的返回值要大,在a表和b表上都有user_no的索引,请问这会是什么原因?