In T-SQL, you summarize data by using the GROUP BY clause within an aggregate query. This clause creates groupings which are defined by a set of expressions. One row per unique combination of the expressions in the GROUP BY clause is returned, and aggregate functions such as COUNT or SUMmay be used on any columns in the query. However, if you want to group the data by multiple combinations of group by expressions, you may take one of two approaches. The first approach is to create one grouped query per combination of expressions and merge the results using the UNION ALLoperator. The other approach is to use the GROUPING SETS operator along with the GROUP BY clause and define each grouping set within a single query.
In this article I’ll demonstrate how to achieve the same results using each method.
Mastering GROUPING SETS makes reporting queries in T-SQL so much more effective.