SQL provides several aggregate functions that allow you to perform calculations on a set of values. Some of the most commonly used aggregate functions are:

1. `COUNT`: This function returns the number of rows in a result set. The syntax for this function is:
``````COUNT(*)
``````

Here is an example:

``````SELECT COUNT(*) FROM employees;
``````

The result of this query will be the number of rows in the `employees` table.

1. `SUM`: This function returns the sum of values in a specified column. The syntax for this function is:
``````SUM(column name)
``````

Here is an example:

``````SELECT SUM(salary) FROM employees;
``````

The result of this query will be the total salary of all employees in the `employees` table.

1. `AVG`: This function returns the average value of a specified column. The syntax for this function is:
``````AVG(column name)
``````

Here is an example:

``````SELECT AVG(salary) FROM employees;
``````

The result of this query will be the average salary of all employees in the `employees` table.

1. `MIN` and `MAX`: These functions return the minimum and maximum values, respectively, of a specified column. The syntax for these functions is:
``````MIN(column name)
MAX(column name)
``````

Here is an example:

``````SELECT MIN(salary) FROM employees;
SELECT MAX(salary) FROM employees;
``````

The result of the first query will be the minimum salary of all employees in the `employees` table, and the result of the second query will be the maximum salary.

In conclusion, SQL provides several aggregate functions for performing calculations on a set of values. These functions are useful for summarizing and analyzing data, and are commonly used in business intelligence and data analysis applications.

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