How do I use T-SQL Group By

Question

I know I need to have (although I don\'t know why) a GROUP BY clause on the end of a SQL query that uses any aggregate functions like count,

Answer 1

To retrieve the number of widgets from each widget category that has more than 5 widgets, you could do this:

SELECT WidgetCategory, count(*)
FROM Widgets
GROUP BY WidgetCategory
HAVING count(*) > 5

The "having" clause is something people often forget about, instead opting to retrieve all their data to the client and iterating through it there.