SQL Practice 5/13

Group rows together

COUNT, MAX, and friends get more useful once you can run them per-group instead of over the whole table. GROUP BY column buckets the rows by every distinct value in that column, then applies the aggregate to each bucket separately - one output row per group.

"How many users per country" is a classic GROUP BY: without it you'd get one number for everyone; with it you get one number for each country. Any column you SELECT alongside an aggregate has to be the column (or one of the columns) you're grouping by - otherwise SQL doesn't know which row's value to show.

Same six-row users table as last lesson.

Your task: return each country and how many users are from it, as total.

You'll practice:

Grouping rows with GROUP BY
Combining a plain column with an aggregate in the same SELECT

-- Return each country and how many users are from it, as `total`.
SELECT country FROM users;