sql语句的问题.

--try ...
--table's name is tbl .
select auther ,case when song is null then (select top 1 song from tbl where song
is not null and auther =a.auther order by song ) else song end as [song]
from tbl a

用表变量@ta测试:--(把@ta变为表名就行了)
declare @ta table (author varchar(10), song varchar(30))
insert @ta
select 'john', 'yestody once more'
union all select 'john', null
union all select 'john', null
union all select 'wubai', 'luo wei d shenglin'
union all select 'wubai', null
union all select 'wubai', null

select author,
song=case when song is null then (select top 1 song from @ta where author=a.author)else song end
from @ta a

（所影响的行数为 6 行）

author song
---------- ------------------------------
john yestody once more
john yestody once more
john yestody once more
wubai luo wei d shenglin
wubai luo wei d shenglin
wubai luo wei d shenglin

（所影响的行数为 6 行）

条件判断,如果song的值是null的话从tb1取出第一个符合条件的值作为song的值,否则(不为空)用song的值作为列的值.

case when

-------------
简洁点的case when 相当于 C里面的 (？：)