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Jan 21, 2025 am 06:27 AM

How Do One-to-One, One-to-Many, and Many-to-Many Database Relationships Work?

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-- Table 1: Student
CREATE TABLE Student (
    student_id INT PRIMARY KEY,
    first_name VARCHAR(255),
    last_name VARCHAR(255),
    address_id INT
);

-- Table 2: Address
CREATE TABLE Address (
    address_id INT PRIMARY KEY,
    address VARCHAR(255),
    city VARCHAR(255),
    zipcode VARCHAR(10),
    student_id INT UNIQUE
);

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-- Table 1: Teacher
CREATE TABLE Teacher (
    teacher_id INT PRIMARY KEY,
    first_name VARCHAR(255),
    last_name VARCHAR(255)
);

-- Table 2: Class
CREATE TABLE Class (
    class_id INT PRIMARY KEY,
    class_name VARCHAR(255),
    teacher_id INT
);

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-- Table 1: Student
CREATE TABLE Student (
    student_id INT PRIMARY KEY,
    first_name VARCHAR(255),
    last_name VARCHAR(255)
);

-- Table 2: Class
CREATE TABLE Class (
    class_id INT PRIMARY KEY,
    name VARCHAR(255)
);

-- Junction Table: Student_Class
CREATE TABLE Student_Class (
    class_id INT,
    student_id INT,
    PRIMARY KEY (class_id, student_id)
);

Student_Class ???? ???? ?? ??? ?? ??? ??? ? ????.

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-- Students in a specific class:
SELECT s.student_id, s.last_name
FROM Student_Class sc
JOIN Student s ON s.student_id = sc.student_id
WHERE sc.class_id = 1;

-- Classes attended by a specific student:
SELECT c.class_id, c.name
FROM Student_Class sc
JOIN Class c ON c.class_id = sc.class_id
WHERE sc.student_id = 2;

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