请问一个mysql查询有关问题，送上100分

create temporary table A
select 1 as uid, 1 as mid, 100 as cash
union select 2, 2, 105
union select 3, 3,  98
union select 4, 4,  55
union select 5, 5,  60
union select 6, 6,  70;

create temporary table B
select 1 as uid, 1 as mid, 101 as cash, 100 as  number
union select 2,     1,   100,    100
union select 3,     2,   105,    200
union select 4,     2,   105,    300
union select 5,     3,   60,     300
union select 6,     3,   98,     300;

select uid,mid, cash, (select sum(number) from B where mid=A.mid and cash=A.cash) from A

select a.uid, a.mid, a.cash, sum(b.number) from testa as a left join testb as b on a.mid=b.mid and a.cash = b.cash group by a.mid, a.cash