Unique Customer Countries — DISTINCT in SQL

The problem

Brightlane's growth team is building a regional marketing strategy and needs to identify which countries have registered customers.

Write a query to return each country represented in the customer base, with no duplicates.

Assumptions:

The customers table contains every customer Brightlane has on file.
Many customers share the same country, so the raw country column has heavy duplication.

Output:

One row per distinct country, with a single column country.

Schema · ecommerce 5 tables

categories

id integer

name text

parent_id? integer

products

id integer

name text

category_id integer

price numeric

stock_qty integer

attributes? jsonb

order_items

id integer

order_id integer

product_id integer

quantity integer

unit_price numeric

customers

id integer

name text

email text

city? text

country text

created_at timestamptz

is_active boolean

orders

id integer

customer_id integer

ordered_at timestamptz

status text

total_amount numeric

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Worked solution Try it yourself first

Solution query

SELECT DISTINCT
  country
FROM
  customers

The shape

DISTINCT on country collapses the heavily duplicated column down to its unique values — 22 rows out of however many thousand customers, one per country the growth team actually has presence in.

Clause by clause

SELECT DISTINCT country names the one column the dropdown needs and tells SQL to deduplicate the output. The keyword sits between SELECT and the column list; it applies to the whole row that comes back, not just to country in isolation. With only one column in the SELECT list, that distinction doesn't bite here, but it's the rule that matters as soon as a second column gets added.
FROM customers is the row source — every customer Brightlane has on file. Each row contributes its country value to the candidate set, and DISTINCT runs across that set to produce the unique enumeration.

The result reads like a value space, not a customer list. Twenty-two rows, one per country represented in the base — US, GB, DE, and so on — which is exactly the input the regional marketing strategy needs.

You practiced collapsing a duplicated column down to its unique values with DISTINCT. The recurring shape: any time a single attribute repeats across many rows and the question is "what values exist," DISTINCT is the one-keyword answer.

Return each country represented in the customer base, with no duplicates

The shape

Clause by clause

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