In database management, duplicate data is an inevitable byproduct of complex data entry, multiple joins, or redundant logging. The SQL DISTINCT keyword is the primary tool used to filter out these duplicates and return only unique values from a query. Whether you are building a reporting dashboard or cleaning a dataset for machine learning, understanding the nuances of DISTINCT is essential for data integrity.

What is the SQL SELECT DISTINCT Statement?

The SELECT DISTINCT statement is used to return only different (unique) values. Within a table, a column often contains many duplicate values; and sometimes you only want to list the unique values. The DISTINCT keyword acts as a filter that examines the result set after the initial data retrieval and discards rows that are identical to ones already processed.

Basic Syntax

The most fundamental use of DISTINCT is on a single column. The syntax is straightforward: