Database Systems - Foreign Key Example - How to use the FOREIGN KEY Constraint
The FOREIGN KEY constraint specifies which column to use as the foreign key, which is typically a primary key to another table.
You can apply rules or constraints to your database table when you create it with CREATE TABLE, or later on with ALTER TABLE.
Example:
CREATE TABLE Director (
DirectorID SMALLINT UNSIGNED AUTO_INCREMENT,
FirstName VARCHAR(50),
LastName VARCHAR(50),
PRIMARY KEY (DirectorID)
);
CREATE TABLE Movie (
MovieID SMALLINT UNSIGNED AUTO_INCREMENT,
DirectorID SMALLINT UNSIGNED,
Title VARCHAR(100),
PRIMARY KEY (MovieID),
FOREIGN KEY (DirectorID) REFERENCES Director(DirectorID)
);
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