批量更新语句
客户表(customer)
卡号(cardno) 卡内金额(Fare)

消费明细表(consume)
卡号(cardno) 消费金额(confare)

充值明细表(cashrec)
卡号(cardno) 充值金额(cashfare)

需要更新客户表中卡内金额
卡内金额=充值金额汇总-消费金额汇总
帮忙看这个SQL语句怎么写
[解决办法]

if OBJECT_ID('customer') is not null drop table customer
create table customer
(
cardno int,
Fare decimal(10,2)
)
if OBJECT_ID('consume') is not null drop table consume
create table consume
(
cardno int,
confare decimal(10,2)
)
if OBJECT_ID('cashrec') is not null drop table cashrec
create table cashrec
(
cardno int,
cashfare decimal(10,2)
)

insert into customer
select 1,20 union
select 2,40 union
select 3,70 union
select 4,70 

insert into consume
select 1,20 union
select 1,40 union
select 2,70 union
select 2,70 

insert into cashrec
select 1,10 union
select 1,30 union
select 2,60 union
select 2,80 
select * from customer

go

with cte 
as
(
select  t.cardno,(case when SUM(t2.cashfare)-SUM(t1.confare) is not null then SUM(t2.cashfare)-SUM(t1.confare) 
else sum(t.Fare) end) Fare
from 
customer t 
left join consume t1 on t.cardno=t1.cardno
left join cashrec t2 on t.cardno=t2.cardno
group by t.cardno
)
update customer set Fare=
(
select cte.Fare
from 
cte
where cte.cardno=customer.cardno
)
select * from customer