Kuidas rakendada füüsilisel tasandil ühe-ühele suhet kahe tabeli vahel?

At the physical level, a one-to-one relationship between two tables is implemented in several ways:

1. Shared primary key — both tables have the same primary key value, and in one of them, this key also serves as a foreign key to the other table.

2. Unique foreign key — in one table, a foreign key to another table is created with a UNIQUE constraint, ensuring that each record corresponds to at most one record in the related table.

Example with shared primary key:

CREATE TABLE Person (
    PersonID INT PRIMARY KEY,
    Name VARCHAR(100)
);

CREATE TABLE Passport (
    PersonID INT PRIMARY KEY,
    PassportNumber VARCHAR(50),
    FOREIGN KEY (PersonID) REFERENCES Person(PersonID)
);

Here, each record in Person can have at most one record in Passport, and vice versa.