In this SQL tutorial I will cover SQL GROUP BY clause and give examples of how to use it. I will use SQL Server 2008 R2, but the examples in this tutorial should work with all SQL Server versions and some other databases. I will start with short and easy examples and explanations and move on to common group by questions that are slightly more involved.
Below is group by syntax in the simpliest form:
GROUP BY FieldName
Group By allows us to group rows together and additionally perform aggregate calculation which works on a group of rows. Let me first give you a simple example of what group by does using one field. I will use Customer table and group all customers by Country in other words I want to show all unique values that exist in Country Field, that is how group by works. See below example code with results (before and after)