Aggregate Functions : COUNT(), SUM(), AVG(), MIN(), MAX() | SQL- MySQL | Belayet Hossain

Aggregate Functions in SQL :

Aggregate functions in SQL perform calculations on a set of rows and return a single summary value. These functions are commonly used with the GROUP BY clause to group rows based on one or more columns.

?? Common Aggregate Functions

1. COUNT() : Returns the number of rows.
2. SUM() : Calculates the total sum of a numeric column.
3. AVG() : Returns the average value of a numeric column.
4. MIN() : Returns the smallest value in a column.
5. MAX() : Returns the largest value in a column.

→ Syntax

SELECT aggregate_function(column_name)

FROM table_name

?? 1.? COUNT () : Returns the number of rows in a table.

→ Example: Count the number of student in the student table.

→ Syntax:

select count(*) as total_student

from student

→ Output: total_student - 5

?? 2.????? AVG () Function: Returns the average value of a numeric column.

→ Example: Find the average salary of employees in the employee table.

→ Syntax:

select avg(salary) as Avg_Salary

from employee

→ Output: Avg_Salary - 38,750

?? 3.? SUM () : Calculates the total sum of a numeric column.

→ Example: Calculate the total salary of all employees in the employee table.

→ Syntax:

select sum(salary) as Total_salary

from employee

→ Output: Total_salary 155,000

?? 4.????? MIN () : Returns the smallest value in a column.

→ Example: Find the minimum salary in the Employees table.

→ Syntax:

select min(salary) as Min_Salary

from employee

→ output: Min_Salary 10,000

?? 5.????? MAX () : Returns the maximum value in a column.

→ Example: Find the maximum salary in the Employees table.

→ Syntax:

select max(salary) as Max_Salary

from employee

→ output: Max_Salary 55,000

?

?? Key Points

1. Aggregate functions ignore NULL values (except COUNT(*)).
2. Combine with GROUP BY for grouped results.
3. Use HAVING for filtering aggregated data (not WHERE).

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