select COUNT(*),OriginalOrderNo,sku from (
select OriginalOrderNo,
stuff((select ','+Sku from dbo.T_OMSRefundOrderProduct sp WITH(NOLOCK) WHERE sp.OMSRefundOrderId =a.Id for xml path('')), 1, 1, '') sku
from T_OMSRefundOrder a ) b where b.sku is not null
group by OriginalOrderNo,sku
having COUNT(*)>1