The DISTINCT command removes duplicated data rows from a SELECT query

SELECT DISTINCT field FROM tablename;

Example

customerId	firstName	lastName	address	city	country
1	Ursa	Vasquez	P.O. Box 878, 8416 Nullam St.	Worcester	United States
2	Quyn	Meyer	P.O. Box 670, 7155 Tincidunt St.	Price	Canada
3	Orli	Klein	4981 Gravida St.	Barrow-in-Furness	United Kingdom
4	Tallulah	Hines	6279 Pellentesque Street	Omaha	United States
5	Joel	Ross	P.O. Box 842, 4634 Egestas Avenue	Clovenfords	United Kingdom
6	Charlotte	Ramos	794-1654 A Rd.	Akron	United States
7	Dennis	Avery	P.O. Box 506, 4804 Molestie Avenue	Matlock	United Kingdom
8	Igor	Malone	6627 Porttitor Rd.	Irvine	United Kingdom
9	Connor	Witt	5979 Vel St.	Tain	United Kingdom
10	Karen	Marquez	Ap 524-1173 Metus. Road	Annapolis Royal	Canada

Without `DISTINCT`

SELECT country FROM customers;

SELECT DISTINCT country FROM customers;