create table a(acno varchar(10),acname varchar(10))
insert into a values('12345', 'abcde')
insert into a values('12345', null   )
insert into a values('12345', 'abcde')
insert into a values('12344', 'bcdef')
go

update a set acname = (select top 1 acname from a where acno = t.acno and acname <> '' and acname is not null) from a t where acname = '' or acname is null

select * from a
/*
acno       acname     
---------- ---------- 
12345      abcde
12345      abcde
12345      abcde
12344      bcdef

（所影响的行数为 4 行）
*/

drop table a

------解决方案--------------------

前面一个有错
SQL code

update table_name
set acname = (select top 1 t.acname from table_name t where t.acno = table_name.acno and t.acname is not null)
where acname is null