FOREIGN KEY CONCEPTS

Answer 1

A FOREIGN KEY 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 table containing the foreign key is called the child table, and the table containing the candidate key is called the referenced or parent table.
CREATE TABLE Orders (
OrderID int NOT NULL PRIMARY KEY,
OrderNumber int NOT NULL,
PersonID int FOREIGN KEY REFERENCES Persons(PersonID)
);
CREATE TABLE Orders (
OrderID int NOT NULL,
OrderNumber int NOT NULL,
PersonID int,
PRIMARY KEY (OrderID),
CONSTRAINT FK_PersonOrder FOREIGN KEY (PersonID)
REFERENCES Persons(PersonID)
);