SQL Functions

This page covers SQL Functions.

Similarly to other programming languages, SQL allows the use of functions.

Functions perform operations on values and return the result. We cover only some basic SQL built-in functions in this section.

For more details functions here.

This tutorial encompasses:

Let’s use the table “student_info” from the previous tutorials.

id	firstName	lastName	age
1	John	Smith	21
2	Patrick	Casey	26
3	Sam	Adams	19
4	Mike	Garcia	NULL
5	Patrick	Dumont	21

Min and Max

These functions are very straightforward.

The “min” function returns the smallest value in a column, and the “max” returns the largest value in a column.

SELECT MIN(age) FROM student_info;
-- Output: 19
SELECT MAX(age) FROM student_info;
-- Output: 26

We have students with the ages of 21, 26, 19, NULL, and 21. NULL is empty. Therefore the smallest is 19 and the largest 26.

The “average” function does what it says.

This function returns the average value from a selected column.

Below is an example.

SELECT AVG(age) FROM student_info;
-- Output: 21

The average can be found by adding up all numbers and then dividing by the count of numbers.

The “sum” function returns the total sum in a column.

The following is an example of “sum”.

SELECT SUM(age) FROM student_info;
-- Output: 87

The ages are 21, 26, 19, NULL, and 21. NULL is empty. We add up all numbers and get the total number of 87.

The “count” function the number of elements in a column.

Below is an example.

SELECT COUNT(age) FROM student_info;
-- Output: 4

There are 5 cells in the “age” column. But NULL refers to an empty cell. Therefore, the count of all ages is 4.