SQL SELECT DISTINCTL

• 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.

Use of DISTINCT in SQL:

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 duplicate values from the output.