SQL FOREIGN KEY Keyword

❮ SQL Keywords

constraint is a key used to link two tables together. A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table.

The following SQL creates a FOREIGN KEY on the "PersonID" column when the "Orders" table is created:

( OrderID int NOT NULL, OrderNumber int NOT NULL, PersonID int, PRIMARY KEY (OrderID), FOREIGN KEY (PersonID) REFERENCES Persons(PersonID)

( OrderID int NOT NULL PRIMARY KEY, OrderNumber int NOT NULL,

To allow naming of a FOREIGN KEY constraint, and for defining a FOREIGN KEY constraint on multiple columns, use the following SQL syntax:

( OrderID int NOT NULL, OrderNumber int NOT NULL, PersonID int, PRIMARY KEY (OrderID), CONSTRAINT FK_PersonOrder FOREIGN KEY (PersonID)

To create a FOREIGN KEY constraint on the "PersonID" column when the "Orders" table is already created, use the following SQL:

ADD FOREIGN KEY (PersonID)

To allow naming of a FOREIGN KEY constraint, and for defining a FOREIGN KEY constraint on multiple columns, use the following SQL syntax:

To drop a FOREIGN KEY constraint, use the following SQL:

❮ SQL Keywords