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Last modified: November 6, 2025


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Mandatory Relationship

normal relationship

CREATE TABLE Product (
    product_id INT PRIMARY KEY,
    pname VARCHAR(50),
    category VARCHAR(50),
    company_id INT,  --(can be NULL)
    FOREIGN KEY (company_id)
  REFERENCES Company(company_id)
);


mandatory relationship

CREATE TABLE Product (
    product_id INT PRIMARY KEY,
    pname VARCHAR(50),
    category VARCHAR(50),
    company_id INT NOT NULL,  --(cannot be NULL)
    FOREIGN KEY (company_id)
  REFERENCES Company(company_id)
);