This stored procedure, which I created in the AdventureWorks2017 database, has two parameters: @CustomerID and @SortOrder. The first parameter, @CustomerID, affects the rows to be returned. If a specific customer ID is passed to the stored procedure, then it returns all the orders (top 10) for this customer. Otherwise, if it’s NULL, then the stored procedure returns all orders (top 10), regardless of the customer. The second parameter, @SortOrder, determines how the data will be sorted—by OrderDate or by SalesOrderID. Notice that only the first 10 rows will be returned according to the sort order.
So, users can affect the behavior of the query in two ways—which rows to return and how to sort them. To be more precise, there are 4 different behaviors for this query:
1. Return the top 10 rows for all customers sorted by OrderDate (the default behavior)
2. Return the top 10 rows for a specific customer sorted by OrderDate
3. Return the top 10 rows for all customers sorted by SalesOrderID
4. Return the top 10 rows for a specific customer sorted by SalesOrderID
Let’s test the stored procedure with all 4 options and examine the execution plan and the statistics IO.
This is quite common for reporting procedures and Guy shares several patterns, some of which work better than others.