SQL SELECT DISTINCT

Chapter 4 of 40 · Estimated read time: 5 min

The SELECT DISTINCT statement returns only unique values in the result set — duplicate rows are removed. Use it when you want to see what distinct values exist in a column.

Syntax

Example 1 — Without vs With DISTINCT

-- Without DISTINCT
-- (shows all rows)
SELECT category
FROM products;

-- With DISTINCT
-- (unique values only)
SELECT DISTINCT category
FROM products;

Example 2 — DISTINCT on Multiple Columns

When you use DISTINCT on multiple columns, it returns unique combinations of those columns:

SELECT DISTINCT customer_id, product_id
FROM orders;

Example 3 — COUNT DISTINCT

Combine DISTINCT with COUNT to count unique values — one of the most common patterns in analytics:

-- How many unique categories do we have?
SELECT COUNT(DISTINCT category) AS category_count
FROM products;
-- Result: 3

-- How many unique customers placed an order?
SELECT COUNT(DISTINCT customer_id) AS active_customers
FROM orders;
-- Result: 4 (C05 never ordered)

-- How many unique products were ordered?
SELECT COUNT(DISTINCT product_id) AS products_ordered
FROM orders;
-- Result: 6

Example 4 — List All Cities Customers Are From

SELECT DISTINCT city
FROM customers
ORDER BY city;

-- 1.
SELECT DISTINCT supplier_id FROM products;

-- 2.
SELECT COUNT(DISTINCT customer_id) AS unique_customers FROM orders;

-- 3.
SELECT DISTINCT category, supplier_id FROM products ORDER BY category;