SQL Aggregate functions, Order By, Join Query

এই Lisson এ  SQL Aggregate functions SUM(), AVG(), COUNT(), MAX(), MIN(), Order By, Join Query এর ব্যবহার দেখব।

Aggregate Functions:

SELECT MIN(age)
FROM students;

SELECT MAX(age)
FROM students;

SELECT COUNT(age)
FROM students;

SELECT AVG(age)
FROM students;

SELECT SUM(age)
FROM students;

SELECT * FROM students
WHERE age = (SELECT MAX(age) FROM students)

Group By:

SELECT class, COUNT(id)
FROM students
GROUP BY class;

SELECT class, MAX(age) AS student_age
FROM students
GROUP BY class;

Union:

SELECT id, name 
FROM students
WHERE age = 21
UNION
SELECT id, name 
FROM students
WHERE age = 12;

Join Query:

SELECT * FROM students
JOIN classes ON classes.id = students.class_id;

SELECT * FROM students
INNER JOIN classes ON classes.id = students.class_id;


SELECT * FROM students
LEFT JOIN classes ON classes.id = students.class_id;

SELECT * FROM students
RIGHT JOIN classes ON classes.id = students.class_id;


SELECT * FROM students
LEFT JOIN classes ON classes.id = students.class_id
UNION
SELECT * FROM students
RIGHT JOIN classes ON classes.id = students.class_id;


SELECT * FROM students
LEFT JOIN classes ON classes.id = students.class_id
UNION ALL
SELECT * FROM students
RIGHT JOIN classes ON classes.id = students.class_id;