for xml path

FOR XML PATH 문을 활용해서 동일계층의 컬럼값을 한줄로..

with custgroups as
(
 select customerid,
  (select cast(employeeid as varchar(10)) + ';' as [text()] (의미없음-현혹되면 안됨)
   from ( select distinct employeeid from dbo.orders as O
    where O.customerid = c.customerid) as D
   order by employeeid
   for xml path('')) as custemps
  from dbo.customers as C
)
select customerid,
 case when custemps is null then null else min(customerid) over (partition by custemps) end as grp
from custgroups
order by grp, customerid;