SQL SELECT DISTINCT Statement

The SELECT DISTINCT statement in SQL is used to retrieve only unique values from one or more columns in a table. It removes duplicate rows from the result set, giving you a concise list of distinct entries.

SELECT DISTINCT: Definition and Usage

SELECT DISTINCT is incredibly useful when you only need a list of unique values and don't want to see repeated entries. This is commonly used when you want a list of all available options for a particular column (for example: unique countries, product categories, or any other attribute where you're interested only in the distinct values).

Syntax

SELECT DISTINCT column1, column2, ...
FROM table_name;
      

Example Database

Let's use a sample 'Customers' table for our examples:

Examples

Selecting Distinct Countries

This query retrieves a list of unique countries from the 'Customers' table.

SELECT DISTINCT Country FROM Customers;
      

Country
-------
Germany
Mexico
UK
Sweden
      

Selecting All Countries (Without DISTINCT)

This query, without DISTINCT, returns all countries, including duplicates.

SELECT Country FROM Customers;
      

Country
-------
Germany
Mexico
Mexico
UK
Sweden
      

Counting Distinct Countries

This uses COUNT(DISTINCT) to get the number of unique countries. (Note: COUNT(DISTINCT) is not supported by MS Access.)

SELECT COUNT(DISTINCT Country) FROM Customers;
      

SELECT Count(*) AS DistinctCountries
FROM (SELECT DISTINCT Country FROM Customers);
      

DistinctCountries
-----------------
4