See whether a groupped item have more than one value in a database column
You can either use an IN clause with an intersect

select *
from product_lines
where sku in (select sku 
              from product_lines
              where discount &gt; 0
              intersect
              select sku
              from product_lines
              where discount = 0);


Using exists might be faster with SQL Server:

select *
from product_lines p1
where exists (select *
              from product_lines p2
              where p2.discount &gt; 0
               and p2.sku = p1.sku)
  and exists (select * 
              from product_lines p3
              where p3.sku = p1.sku
                and p3.discount = 0);