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SQL DISTINCT

In this tutorial, you will learn how to remove duplicate data in the result set using the SQL DISTINCT keyword.

As default SELECT statement will not remove duplicates in the result set.

Sometimes you may be in situation when you have mutiple duplicate rows in a table and you want to remove these duplicate values, then you can specify the keyword DISTINCT directly after the SELECT keyword. 

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Syntax

The basic syntax of the DISTINCT statement to select all columns, can be given with:

				
					SELECT DISTINCT column_names
FROM table_name
				
			

Examples

To understand the SELECT statement in a better way, let’s look at the following customers table in our tutorial database:

Customers
customer_id first_name last_name country score
1 Maria Cramer Germany 350
2 John Steel USA 900
3 Georg Pipps UK 750
4 Martin Müller Germany 500
5 Peter Franken USA NULL

Now, let’s check out some examples that demonstrate how it actually works.

We have the following task be to solve using SQL statements

List all countries of all customers without duplicates

First, lets retrive all data from country column in customers table by executing the following SQL Statement:

				
					SELECT country
FROM customers
				
			

After executing the above query, you’ll get the result set something like this:

country
Germany
USA
UK
Germany
USA

As you can see the output contains a list of all countries of customers, we are almost there but the problem you’ll find the country “Germany” and “USA” twice and that is duplicate in the result, which is not good.

If you see the result carefully, in column country there are only 3 countries “Germany”, “UK”, and “USA”.

Well, let’s fix it, by just adding the magic word DISTINCT like this:

				
					SELECT DISTINCT country
FROM customers
				
			

After executing the above query, you’ll get the result set something like this:

country
Germany
USA
UK

As you see this time there is no duplicate values and we accomplished the task by having a list of all countries of customers excluding without having duplicates.

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