Single-column grouping

Group by one column.

Single-column grouping is the simplest form. Each distinct value becomes a group.

SELECT city, COUNT(*)
FROM customers
GROUP BY city;

This query gives the customer count per city.

city, COUNT(*) is selected from customers. Rows are grouped by city; aggregate functions are computed per group.

Single-column grouping — details

You cannot put non-grouped columns in SELECT; only the group column and aggregates.

For example, SELECT city, name FROM customers GROUP BY city fails; name is not grouped, so it is unclear which customer's name to show.

Group customers by city and count.

Show example solution

SELECT city, COUNT(*)
FROM customers
GROUP BY city;

Add GROUP BY

SELECT city, COUNT(*)
FROM customers
____ city;

Show answer

SELECT city, COUNT(*)
FROM customers
GROUP BY city;