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Customers per region, including unassigned · SQL scenario · D8LooP

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Customers per region, including unassigned

A regional summary counts customers per region. Two customers have no region assigned, and they still need to appear rather than being quietly dropped. Return one row per region, unassigned last.

Result columns · in this order

`region`	The region, or 'unassigned' when none is set.
`customers`	How many customers are in it.

How to approach it

Group by the raw column and label the missing value in the SELECT.

Sample input

shop_customersOne row per customer. region is NULL when unassigned.

customer_id	full_name	region	signed_up_on
c1	Ada Okafor	North	2025-11-02
c2	Bo Lindqvist	null	2025-12-14
c3	Chen Wei	South	2026-01-03
c4	Dara O'Neill	North	2026-01-20
c5	Eve Marsh	null	2026-02-01

5 rows — all rows shown.

Expected output

The exact result your query should return for this input.

region	customers
North	2
South	1
unassigned	2

3 rows — all rows shown.

Constraints

1Every customer is counted exactly once, so the counts add up to 5.
2Customers with no region form a single row labelled unassigned, not one row each.
3That row sorts last.
4Do not filter out the NULL region.

Worked example

Bo Lindqvist and Eve Marsh both have a NULL region. GROUP BY region puts the two of them into one group, and COUNT(*) reports 2. That is worth pausing on, because NULL = NULL is not true — joining the table to itself on region matches none of those rows. Grouping and comparison treat NULL differently on purpose: GROUP BY and DISTINCT treat all NULLs as the same value, while = treats each as unknown.

What this tests

That GROUP BY collects all NULLs into a single group even though NULL = NULL is never true — an asymmetry that decides whether missing data shows up in a report or disappears from it.

SQL

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