MySQL DISTINCT

By default, a SELECT query returns all rows — including duplicates. The DISTINCT keyword tells MySQL to return only unique values, eliminating repeated entries from the result set. This is especially useful when you want to see a list of all possible values in a column without seeing the same value appear multiple times.

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Syntax

SELECT DISTINCT column1, column2
FROM table_name;

DISTINCT is placed immediately after SELECT and applies to all the columns listed.

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Sample Table

id	name	city	age
1	Rahim Uddin	Dhaka	22
2	Sara Begum	Chittagong	20
3	Karim Ali	Sylhet	23
4	Nila Akter	Dhaka	21
5	Rafi Hossain	Rajshahi	24
6	Tania Islam	Dhaka	22

Notice that Dhaka appears three times and age 22 appears twice.

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DISTINCT on a Single Column

Get the list of unique cities — each city appears only once regardless of how many students are from there:

SELECT DISTINCT city FROM students;

city
Dhaka
Chittagong
Sylhet
Rajshahi

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Without DISTINCT — For Comparison

Without DISTINCT, Dhaka would appear three times:

SELECT city FROM students;

city
Dhaka
Chittagong
Sylhet
Dhaka
Rajshahi
Dhaka

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DISTINCT on Multiple Columns

When you use DISTINCT with multiple columns, it removes rows where the combination of all listed columns is a duplicate:

SELECT DISTINCT city, age FROM students;

city	age
Dhaka	22
Chittagong	20
Sylhet	23
Dhaka	21
Rajshahi	24

Dhaka still appears twice because the combination (Dhaka, 22) and (Dhaka, 21) are different pairs. The row with Tania Islam (Dhaka, 22) is deduplicated against Rahim Uddin's identical combination.

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COUNT DISTINCT

Combine DISTINCT with COUNT to count how many unique values exist in a column:

-- How many unique cities do our students come from?
SELECT COUNT(DISTINCT city) AS unique_cities FROM students;
-- Returns: 4

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DISTINCT and NULL

If a column contains multiple NULL values, DISTINCT treats all of them as a single unique value and returns only one NULL in the output:

SELECT DISTINCT phone FROM students;
-- If phone has 3 NULL rows, only one NULL appears in the result

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Key Points to Remember

• SELECT DISTINCT removes duplicate rows from the result set.
• Place DISTINCT immediately after SELECT.
• With multiple columns, DISTINCT deduplicates based on the combination of all listed columns.
• Use COUNT(DISTINCT column) to count the number of unique values in a column.
• Multiple NULL values are treated as a single unique entry by DISTINCT.