SQL SELECT DISTINCT

The DISTINCT keyword in SQL eliminates all duplicate records from the result returned by the SQL query.
The DISTINCT keyword is used in combination with select statements.
Only unique records are returned when the DISTINCT keyword is used while fetching records from a table having multiple duplicate records.
DISTINCT can also be used along with aggregate SQL functions like COUNT, MAX, SUM, AVG etc.
DISTINCT operates not only on a single column of a table but also has support for multiple columns of a table.
DISTINCT in SQL will eliminate those rows where all the selected columns are identical.

Syntax:

SELECT DISTINCT column _ name
FROM table _ name;

A DISTINCT clause in SQL can be applied to any valid SELECT query, where it will filter out all rows that are not unique in terms of all selected columns.
column _ name: name of the column on which we want to apply the DISTINCT clause.

table _ name: name of the table from which we want to retrieve the records.

Let us consider the following STUDENTS table, containing roll no, name, and age :

First, write a SQL query to return all student's ages, including duplicate values:

Example:

SELECT Age as age
FROM students;

Output:

The above SQL query returns the age of every student, including duplicate value ie., 18 occurs twice in the age column of the student's table.
To remove these duplicate age values, we can use DISTINCT in the SQL clause before the column name in combination with the SELECT query

Example:

SELECT DISTINCT age as age
FROM Students;

Output:

The above SQL query returns only the unique ages from the student's table
Duplicate value 18 is not returned because the DISTINCT clause eliminates all the identical values from the output.