SQL · Chapter 4 of 42

SELECT DISTINCT

`SELECT DISTINCT` returns only unique combinations of the listed columns.

Use it to see 'what values exist' in a column.

Syntax

SELECT DISTINCT column FROM table;

Multiple columns

`DISTINCT col1, col2` treats the pair as one value — a row is duplicate only if BOTH match.

DISTINCT sorts/hashes rows to deduplicate, so it can be slow on huge tables. A GROUP BY often achieves the same.

Example 1 (sql)

SELECT DISTINCT country FROM users;

Output

country
India
USA
UK

List each country once, even if many users share it.

Example 2 (sql)

SELECT DISTINCT country, city FROM users;

Output

country | city
India   | Delhi
India   | Mumbai
USA     | NY

Distinct city+country pairs.

💡 Note: `COUNT(DISTINCT col)` counts unique non-NULL values — a common analytics pattern.