GROUPING ID in SQL Server

/*

UNDERSTANDING THE GROUPING ID IN SQL SERVER.....

IS A FUNCTION THAT COMPUTES THE LEVEL OF GROUPING. GROUPING_ID CAN BE USED ONLY IN THE SELECT <SELECT> LIST, HAVING, OR ORDER BY CLAUSES

WHEN GROUP BY IS SPECIFIED.

*/

DECLARE @T TABLE(REGION VARCHAR(100), NAME VARCHAR(100), AMOUNT DECIMAL(12,2))

INSERT INTO @T

SELECT 'REGION1','NAME1',2000 UNION ALL

SELECT 'REGION1','NAME2',100  UNION ALL

SELECT 'REGION1','NAME3',500  UNION ALL

SELECT 'REGION1','NAME3',3400 UNION ALL

SELECT 'REGION2','NAME1',3233 UNION ALL

SELECT 'REGION2','NAME2',5000 UNION ALL

SELECT 'REGION2','NAME2',5344 UNION ALL

SELECT 'REGION3','NAME1',1200 UNION ALL

SELECT 'REGION3','NAME2',900  UNION ALL

SELECT 'REGION4','NAME1',2540

SELECT * FROM @T

SELECT REGION,NAME,SUM(AMOUNT) AS AMOUNT,GROUPING_ID(REGION) AS [GROUPING] FROM @T

GROUP BY REGION, NAME

WITH ROLLUP

/* SEE THIS LINK FOR EXAMPLE HTTPS://MSDN.MICROSOFT.COM/EN-US/LIBRARY/BB510624.ASPX */