MS SQL Server Interview Question:

Can Multiple Columns Be Used in SQL GROUP BY Clause in MS SQL Server?

Submitted by: Administrator

If you want to break your output into smaller groups, you can specify multiple column names or expressions in the GROUP BY clause. Output in each group must satisfy a specific combination of the expressions listed in the GROUP BY clause. The more columns or expressions entered in the GROUP BY clause, the smaller the groups will be. The tutorial exercise below shows you how to break data into groups per "tag" and per year when they were created. Then the group function COUNT(*) is applied on each group:

SELECT tag, YEAR(created), COUNT(*)
FROM ggl_links GROUP BY tag, YEAR(created)
GO<pre>
tag year(created) count(*)
SQA 2003 1
DEV 2004 1
DBA 2005 1
DBA 2006 1
DEV 2006 1
DBA 2007 1
SQA 2007 1</pre>
So there is only one row in each group.
Submitted by: Administrator