use test
go
create  table #t1(ComId char(2),height char(2))
insert #t1 select 'A1','oo' 
insert #t1 select 'A1','hh' 
go
create  table #t2(ComId char(2),width char(2)) 
insert #t2 select 'A1','T2' 
insert #t2 select 'A1','T3' 
insert #t2 select 'A1','T4'
go

select *,row=1 into #a from #t1 order by ComId
select *,row=1 into #b from #t2 order by ComId
go
declare @ComId char(2),@i int
update #a
set @i=case when ComId=@ComId then @i+1 else 1 end,row=@i,@ComId=ComId

set @i=0
update #b
set @i=case when ComId=@ComId then @i+1 else 1 end,row=@i,@ComId=ComId
go
select
    [ComId]=case when a.row=(select min(row) from #b where ComId=b.ComId) then b.ComId else ''end,
    [height]=isnull(a.height,''),
    b.width
from 
    #b b 
left join
    #a a on b.ComId=a.ComId and b.row=a.row
/*
ComId height width 
----- ------ ----- 
A1    oo     T2
      hh     T3
             T4

（所影响的行数为 3 行）

*/