Aggregate Functions

 

Besides the functions mentioned above, MySQL also comes with a large number of pre-written aggregate functions.

 

An aggregate function is a function that performs calculation on a set of values and returns the result of the calculation as a single value.

 

We can use some of these built-in aggregate functions to perform various calculations on the data in our tables.

 

Let’s look at some of these functions and apply them on our employees table.

 

The calculations below are based on the employees table found in Appendix A.

 

The commonly used aggregate functions in MySQL include:

 

COUNT()

 

The COUNT() function returns the number of the rows in the table.

 

If we pass in * to the function, it returns the total number of rows in the table.

 

If we pass in a column name instead, it returns the number of non NULL values in that column (NULL values are ignored).

 

If we want to remove...