Database Systems

-- Create a table
CREATE TABLE students (
    id INTEGER PRIMARY KEY,
    name VARCHAR(100),
    age INTEGER,
    grade DECIMAL(3,2)
);

-- Insert data
INSERT INTO students (id, name, age, grade) VALUES
(1, 'Alice', 18, 3.8),
(2, 'Bob', 19, 3.5),
(3, 'Charlie', 18, 3.9);

-- Query data
SELECT * FROM students WHERE age = 18;

-- Update data
UPDATE students SET grade = 4.0 WHERE name = 'Alice';

-- Delete data
DELETE FROM students WHERE id = 3;

-- Join tables
SELECT s.name, c.course_name 
FROM students s 
JOIN enrollments e ON s.id = e.student_id
JOIN courses c ON e.course_id = c.id;