Junior — Middle

What is the difference between a primary key and a foreign key in a database, and how are they used?

sobes.tech AI

Answer from AI

Primary Key — is a unique identifier for each record in a database table. It guarantees that each row is unique and allows for quick data retrieval. Usually, a primary key cannot be NULL and must be unique.

Foreign Key — is a field (or set of fields) in one table that references the primary key of another table. It is used to establish and maintain relationships between tables, ensuring data integrity.

Example:

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

CREATE TABLE Orders (
  OrderID INT PRIMARY KEY,
  UserID INT,
  OrderDate DATE,
  FOREIGN KEY (UserID) REFERENCES Users(UserID)
);

Here, UserID in the Users table is the primary key, and UserID in the Orders table is the foreign key that links an order to a specific user.

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