Posted on 2012-04-11
hi experts, can yo explain me with transact sql code this
"You may be asked if non-persisted computed columns can improve performance. Unfortunately the answer to this covers material that is advanced for this point in the course but included here for trainer reference. Computed columns can help with performance, even when they are not persisted and not referenced directly. If you have a predicate like: unitprice * quantity > 2500 Sql Server cannot make any prediction on rows returned but if you create a computed column on unitprice * quantity, even if it is not persisted, SQL Server can and will create a statistic on it, which can lead to a much better plan. And this works, even when you not directly reference the computed column, as the query optimizer recognizes that it is the same expression. "