SQL aggregate functions are used to perform calculations on sets of values and return a single result. They operate on a group of rows and return a single value based on the values in the specified column(s). Here are some commonly used SQL aggregate functions:

- COUNT(): Returns the number of rows that match a specific condition or the total number of rows in a table.

Example:

SELECT COUNT(*) FROM employees;

- SUM(): Calculates the sum of the values in a column.

Example:

SELECT SUM(sales_amount) FROM sales;

- AVG(): Computes the average value of a column.

Example:

SELECT AVG(price) FROM products;

- MAX(): Finds the maximum value in a column.

Example:

SELECT MAX(salary) FROM employees;

- MIN(): Retrieves the minimum value in a column.

Example:

SELECT MIN(quantity) FROM inventory;

- GROUP_CONCAT(): Concatenates the values from a column into a single string, grouped by a specified column.

Example:

SELECT department, GROUP_CONCAT(employee_name) FROM employees GROUP BY department;

- HAVING(): Filters the results of a query based on a condition after using GROUP BY.

Example:

SELECT department, AVG(salary) FROM employees GROUP BY department HAVING AVG(salary) > 50000;

These aggregate functions can be used in conjunction with the SELECT statement to perform calculations and summarize data in a database.