如何修改这条SQL语句？

[softheaded]

update yy_clap set qs_xs=y.qshj
from yy_clap x,(
select yyhm,sum(qs) as qshj from yy_ryye a
where rq>x.rq_hy
group by yyhm
) as y
where x.yyhm=y.yyhm
提示有错误。列前缀 'x' 与查询中所用的表名或别名不匹配。
我的想法是将yy_ryye中的qs合计赋值给yy_clap，条件是yy_ryye中的rq大于yy_clap中的rq_hy，请教该如何写呢？

[iamltd]

update yy_clap set qs_xs=y.qshj
from (select yyhm,sum(qs) as qshj from yy_ryye a
where rq>yy_clap.rq_hy
group by yyhm
) as y
where yy_clap.yyhm=y.yyhm

[子陌红尘]

update yy_clap set qs_xs=(select sum(qs) from yy_ryye where yyhm=yy_clap.yyhm and rq>yy_clap.rq_hy)

[chuifengde]

update yy_clap set qs_xs=(select sum(qs) from yy_ryye
where rq>yy_clap.rq_hy and yyhm=yy_clap.yyhm
group by yyhm)

[子陌红尘]

update yy_clap
set
qs_xs=(select
sum(qs)
from
yy_ryye
where
yyhm=yy_clap.yyhm
and
rq>yy_clap.rq_hy)

[csdnweii]

update yy_clap set qs_xs=y.qshj
from yy_clap x,(
select yyhm,sum(qs) as qshj from yy_ryye a,yy_clap b
where a.rq>b.rq_hy
group by yyhm
) as y
where x.yyhm=y.yyhm

[quanyi]

update yy_clap set qs_xs=y.qshj
from (select yyhm,sum(qs) as qshj from yy_ryye a
where rq>yy_clap.rq_hy
group by yyhm
) as y
where yy_clap.yyhm=y.yyhm

[zicxc]

update yy_clap
set
qs_xs=(select
sum(qs)
from
yy_ryye
where
yyhm=yy_clap.yyhm
and
rq>yy_clap.rq_hy)
where exists (
select 1 from yy_ryye
where
yyhm=yy_clap.yyhm
and
rq>yy_clap.rq_hy
)

好像这样稳妥点，否则没有的更新为null了