PostgreSQL - COUNT DISTINCT

Introduction

In this tutorial, we want to count the number of unique values of a specific column. In order to do this, we use the COUNT function with the DISTINCT keyword.

We have already created the table student with the following data:

Example 1

We want to count the number of different birth years.

In order to do this, we execute the following SQL statement:

SELECT COUNT(DISTINCT(birthyear))
FROM student;

The following selection is returned:

Example 2

We want to count the number of different birth years for female students.

In order to do this, we execute the following SQL statement:

SELECT COUNT(DISTINCT(birthyear))
FROM student
WHERE gender = 'female';

The following selection is returned:

Conclusion

Congratulations! Now you are one step closer to become an AI Expert. You have seen that it is very easy to count the number of unique values of a specific column. We can simply use the COUNT function with the DISTINCT keyword. Try it yourself!