PostgreSQL – DISTINCT Clause

A DISTINCT clause is used in the select statement to return only the distinct values from a data set.

Consider the employee table as shown below:

id	first_name	last_name	department	salary
101	bryan	walker	sales	50,000
102	alex	carpenter	accounts	55,000
103	sam	white	sales	60,000
104	john	barry	sales	54,000
105	bill	wood	accounts	65,000
106	robert	hopkins	support	70,000
107	david	lee	support	72,000
108	jack	sears	support	65,000
109	tom	young	sales	55,000

I would like to query all the departments from the employee table.

SELECT department FROM employee;

department
----------
sales
accounts
sales
sales
accounts
support
support
support
sales

But what if I would like to return each department name only once ? DISTINCT clause does just that. It removes duplicates from the result set.

SELECT DISTINCT department FROM employee;

department
----------
sales
accounts
support

Also check out DISTINCT ON clause and COUNT DISTINCT.