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SQL Server FAQ - Counting Groups Returned with the GROUP BY Clause

By: FYIcenter.com

(Continued from previous topic...)

How To Count Groups Returned with the GROUP BY Clause?

If you use the COUNT(*) function on groups returned with the GROUP BY clause, it will count the number of rows within each group, not the number of groups. If you want to count the number of groups, you can put the GROUP BY query into a subquery and apply the COUNT(*) function on the main query as shown in the following tutorial exercise:

SELECT tag AS Category, YEAR(created) AS Year, 
   COUNT(*) AS Counts FROM fyi_links GROUP BY tag, 
   YEAR(created)
GO
Category   Year   Counts
SQA        2003   1
DEV        2004   1
DBA        2005   1
DBA        2006   1
DEV        2006   1
DBA        2007   1
SQA        2007   1

SELECT COUNT(*) FROM (
   SELECT tag AS Category, YEAR(created) AS Year, 
   COUNT(*) AS Counts FROM fyi_links GROUP BY tag, 
   YEAR(created) ) groups
GO
7

(Continued on next topic...)

1. How To Join Two Tables in a Single Query?
2. How To Write a Query with an Inner Join?
3. How To Define and Use Table Alias Names?
4. How To Write a Query with a Left Outer Join?
5. How To Write a Query with a Right Outer Join?
6. How To Write a Query with a Full Outer Join?
7. How To Write an Inner Join with the WHERE Clause?
8. How To Name Query Output Columns?
9. What Is a Subquery in a SELECT Query Statement?
10. How To Use Subqueries with the IN Operators?
11. How To Use Subqueries with the EXISTS Operators?
12. How To Use Subqueries in the FROM Clause?
13. How To Count Groups Returned with the GROUP BY Clause?
14. How To Return the Top 5 Rows from a SELECT Query?
15. How To Return the Second 5 Rows?
16. How To Use UNION to Merge Outputs from Two Queries Together?
17. How To Use ORDER BY with UNION Operators