Once a table starts getting a lot of data in it, some columns will contain duplicate values. For example, many Individuals share first names and surnames. Most of the time this isn’t a problem. But sometimes you will want to find out how many unique values there are in a table. To do this you can use the DISTINCT keyword.
SELECT DISTINCT(FirstName)FROM Individual
Using the DISTINCT keyword, all customers with a name of “Homer” are counted as one.