ROLLUP and ORDER BY

In one of my previous posts, I discussed on how useful GROUPING function is while writing a ROLLUP/CUBE query.  One more way GROUPING function can help you is – in ordering the results returned by ROLLUP/CUBE queries.

The reason I’m writing this post is, sometime back I seen somebody writing a weird ORDER BY statement to get the desired ordering after writing a query using a ROLLUP operator.  First he didn’t use the GROUPING function in SELECT statement and 2nd his ORDER BY was something like :

ORDER BY CASE ColumnName             WHEN 'Total Of ColumnName'             THEN 'Zzzzzzzz'             ELSE ColumnName          END

Just to get sub total returned by ROLLUP at the bottom of result set.  Well of course if he had the knowledge about GROUPING then he wouldn’t have written such CASE statement in ORDER BY.

As you may know that GROUPING function returns 1 when the row is added by either the CUBE or ROLLUP operator, and 0 when the row is not the result of CUBE or ROLLUP.  So you can easily use this property of the GROUPING for ordering the result set.

Lets have a look at the following example, 1st create some sample data.  

-- create sample table Sales CREATE TABLE Sales ( ID INT, FName VARCHAR(30), Zone VARCHAR(30), Sale INT ) GO -- Load sample data INSERT INTO Sales SELECT 1, 'Mangal', 'East', 20 UNION ALL SELECT 2, 'Mangal', 'East', 150 UNION ALL SELECT 3, 'Mangal', 'West', 50 UNION ALL SELECT 4, 'Ram', 'East', 45 UNION ALL SELECT 5, 'Ram', NULL, 80 UNION ALL SELECT 6, 'Ram', NULL, 40 UNION ALL SELECT 7, 'Sachin', 'West', 50 UNION ALL SELECT 8, 'Sachin', 'West', 40 GO -- Test sample data SELECT Id, FName, Zone, Sale FROM Sales GO

The sample data :

ID	FName	Zone	Sale
1	Mangal	East	20
2	Mangal	East	150
3	Mangal	West	50
4	Ram	East	45
5	Ram	NULL	80
6	Ram	NULL	40
7	Sachin	West	50
8	Sachin	West	40

And here is the expected output :

FName	Zone	Total
Mangal	East	170
Mangal	West	50
Mangal	All Zone	220
Ram	East	45
Ram	Unknown	120
Ram	All Zone	165
Sachin	West	90
Sachin	All Zone	90
All Names	All Zone	475

As you can see in the expected output, all the FNames are ordered in ascending order and their total SUM is at the bottom, same for the Zone column.  For ordering the result in that way just use the GROUPING(column_name) in ORDER BY just before the column_name.  See the following query, esp the ORDER BY clause:

SELECT CASE GROUPING(fname)         WHEN 1 THEN 'All Names'         ELSE ISNULL(Fname, 'Unknown')         END AS FName,         CASE GROUPING(Zone)         WHEN 1 THEN 'All Zone'         ELSE ISNULL(Zone, 'Unknown') END as Zone,         SUM(Sale) AS Total FROM Sales GROUP BY Fname, Zone WITH ROLLUP ORDER BY  GROUPING(fname),FName,GROUPING(Zone),Zone

Simple, isn’t it?  Now you don’t need to write a CASE statement in ORDER BY, just use the GROUPING function.  If you will be doing the ORDERING in application layer, then you will need to get in the GROUPING(fname) and GROUPING(zone) column in the SELECT list as well.

Mangal