? Aggregate Functions in SQL

Aggregate functions perform calculations on a group of rows and return a single value — often used with GROUP BY to summarize data.

? Common Aggregate Functions

? 1. COUNT()

Counts the number of rows (non-null values if used with a column).

SELECT COUNT(*) FROM employees;SELECT COUNT(salary) FROM employees; -- Ignores NULLs

? 2. SUM()

Calculates the total of numeric values.

SELECT SUM(salary) AS total_salary FROM employees;

? 3. AVG()

Finds the average of numeric values.

SELECT AVG(salary) AS avg_salary FROM employees;

? 4. MIN()

Returns the lowest value.

SELECT MIN(salary) AS min_salary FROM employees;

? 5. MAX()

Returns the highest value.

SELECT MAX(salary) AS max_salary FROM employees;

? Example with GROUP BY

Assume a table employees with department and salary:

SELECT department, COUNT(*) AS total_employees, AVG(salary) AS avg_salaryFROM employeesGROUP BY department;

? This will give one row per department with count and average salary.

? Notes:

• All aggregate functions ignore NULL values (except COUNT(*)).

• Often used with GROUP BY or HAVING.

? Tip: Use HAVING to Filter Aggregates

SELECT department, AVG(salary)FROM employeesGROUP BY departmentHAVING AVG(salary) > 50000;

Let me know if you want practice problems, nested aggregate examples, or window function comparison!