This query gives me a result set that condenses the rows with the same country into only one row, while COUNT(*) tells me how many repeated rows there are for each country: Country If I wanted to know how many friends I have in each country, I’d use GROUP BY together with the COUNT() aggregate function: to get a list of the countries where my friends live, including the number of friends living in each country.
I would like to use the information in this table to do some research – e.g. I have created a table called WorldWideFriends that stores data on my friends in different parts of the world: FriendName It’s also good to note that GROUP BY allows you to apply aggregate functions on columns not included in the outstanding subset. GROUP BY 1 ColumnĮach combination of the values of column(s) specified in the GROUP BY clause constitutes a group the SELECT command with a GROUP BY clause displays a single row for each group. Ok, let’s start with a refresher on a simple use case for GROUP BY. This course is also a great way to review basic SQL features if your knowledge is a bit rusty. With each exercise completed, you build confidence in your SQL skills. In each exercise, you get a short explanation and task to solve. It contains 129 hands-on practical exercises. Not familiar with GROUP BY? The best way to learn this and other basic SQL constructions is with our interactive SQL Basics course.
#Mysql case select multiple columns how to#
This article assumes you already know how to use GROUP BY in an SQL query.
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