SQL - Aggregate Functions in SQL

Aggregate functions are used to perform calculations on multiple rows of a table and return a single summarized value. They are commonly used in reports, analytics, and group operations.

Common Aggregate Functions

Syntax Example

SELECT COUNT(*) AS total_employees,

       AVG(salary) AS avg_salary,

       MIN(salary) AS min_salary,

       MAX(salary) AS max_salary,

       SUM(salary) AS total_salary

FROM employees;

Result:

total_employees | avg_salary | min_salary | max_salary | total_salary

----------------------------------------------------------------------

       50       |  45000     |   25000    |   80000    | 2250000

Aggregate Functions with GROUP BY

To calculate aggregates for each group in a table:

SELECT department, COUNT(*) AS dept_count, AVG(salary) AS avg_salary

FROM employees

GROUP BY department;

Result:
Shows employee count and average salary for each department

Key Points

• Aggregate functions ignore NULL values (except COUNT(*))
• Can be combined with GROUP BY for grouped summaries
• Often used with HAVING to filter groups based on aggregate results