GROUPING SETS is less frequently used, but sometimes it can be useful if you're aware of its usefulness.

For example, the result set of this query will be first grouped by the grouping set (Region, Department), and then by City.

SELECT Region, Department, avg(sal) AverageSalary

from tblEmployee

Group BY

GROUPING SETS

(

(Region, Department),

(City)

)

In this case the above select will not return the same ordered result set as

SELECT Region, Department, avg(sal) AverageSalary

from tblEmployee

Group BY

Region, Department, City

Having got the example from the previous post, now you should have understood grouping sets...

Regards,

IgorMi