SQL Server Team-based Development - Red Gate Software

Chapter 11: SQL Refactoring
For a certain year, we need to report:
• the average and maximum monthly sales order values, per territory, per salesperson
• the average monthly sales order value, and numbers sold, per product, per territory.
Clearly, these requirements produce two result sets. In each case, the approach is
the same.
1. Shrink the scope of the problem, mentally, to a single territory and sales person.
2. Break up the request into steps that are easy to solve.
3. Create a solution for each step and use that solution in the next step.
This approach is demonstrated in the reporting query in Listing 11-1, which calculates the
average and maximum monthly sales order values, per territory, per salesperson.
DECLARE @year INT
SELECT @year = 2004
- – Helper date range for efficient query
DECLARE @dateFrom DATETIME ,
@dateTo DATETIME
SELECT
@dateFrom = DATEADD(yyyy, @year – 1900, '19000101') ,
@dateTo = DATEADD(yyyy, 1, @dateFrom)
/*
average sales per territory per person per month
for a given year
*/
/*
Step 1:
query the Sales.SalesTerritory table
for the given year
Step 2:
join to the Sales.SalesOrderHeader to
get SalesPersonID, and other data, in date range
Steps 3-5:
we need SalesPerson Name and Title by joining
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