Core Code
Core Code Modern Dev Handbook

SQL Select Distinct

Use SELECT DISTINCT to return unique values from a column or combination of columns. Avoid duplicate results in your queries.
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SQL SELECT DISTINCT

The SELECT DISTINCT statement is used to return only unique (different) values from a column. It removes duplicate rows from the result set.

Basic Syntax

SELECT DISTINCT column_name
FROM table_name;

Example: Unique Countries

If a customers table contains many customers from the same country, DISTINCT returns each country only once.

SELECT DISTINCT country
FROM customers;

Without DISTINCT, the same country would appear multiple times.

Multiple Columns

DISTINCT applies to the entire row of selected columns. When selecting multiple columns, only completely identical rows are removed.

SELECT DISTINCT country, city
FROM customers;

In this case, duplicate country-city combinations are removed.

COUNT DISTINCT

You can combine DISTINCT with COUNT to see how many unique values exist in a column.

SELECT COUNT(DISTINCT country) AS unique_countries
FROM customers;

When to Use DISTINCT

  • When generating reports that require unique values
  • When building filters (for example, a dropdown list of categories)
  • When analyzing data distribution

Performance Note

DISTINCT may require additional sorting or grouping internally. On large tables, using indexes can significantly improve performance.

Next Step

Continue with SQL WHERE to learn how to filter records based on conditions.

SQL Where →