Junior — Middle

Can you explain what a one-to-one relationship means in databases?

sobes.tech AI

Answer from AI

A one-to-one relationship in databases means that each record in one table corresponds to exactly one record in another table, and vice versa.

For example, you have a Users table and a Profiles table. If each user has only one profile, and each profile belongs to only one user, then a one-to-one relationship is established between these tables.

This relationship is usually implemented using a foreign key with a unique constraint to ensure the uniqueness of the association.

Example in SQL:

CREATE TABLE Users (
    UserId INT PRIMARY KEY,
    UserName VARCHAR(100)
);

CREATE TABLE Profiles (
    ProfileId INT PRIMARY KEY,
    UserId INT UNIQUE,
    Bio TEXT,
    FOREIGN KEY (UserId) REFERENCES Users(UserId)
);

Here, UserId in the Profiles table with a UNIQUE constraint guarantees that each user has no more than one profile.

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