SQL Aggregate Functions – COUNT, SUM, AVG, MIN, MAX
Aggregate Functions in SQL are used to perform calculations on multiple rows of a table and return a single value. They are often used with GROUP BY or HAVING clauses to summarize data.
1. COUNT()
Definition: Returns the number of rows that match a specified condition.
SELECT COUNT(*) AS total_students FROM Student;
Counts all students in the Student table.
2. SUM()
Definition: Returns the total sum of a numeric column.
SELECT SUM(salary) AS total_salary FROM Employee;
Calculates the total salary of all employees.
3. AVG()
Definition: Returns the average value of a numeric column.
SELECT AVG(age) AS average_age FROM Student;
Finds the average age of students.
4. MIN()
Definition: Returns the smallest value in a column.
SELECT MIN(salary) AS lowest_salary FROM Employee;
Finds the lowest salary among employees.
5. MAX()
Definition: Returns the largest value in a column.
SELECT MAX(salary) AS highest_salary FROM Employee;
Finds the highest salary among employees.
Lab Practice Tasks
- Count the total number of students in the Student table.
- Calculate the total and average salary of employees.
- Find the minimum and maximum ages of students.
- Use GROUP BY with COUNT to find the number of students in each department.
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