Q 8. What do you mean by foreign key?
Ans : A Foreign key is a field that can uniquely identify each row in another table. And this constraint is used to specify a field as a Foreign key. That is this
field points to the primary key of another table. This usually creates a kind of link between the two tables.
Consider the two tables as shown below:
Orders:
Customers:
As we can see clearly, that the field C_ID in the Orders table is the primary key in the Customers’ table, i.e. it uniquely identifies each row in the Customers table.
Syntax:
CREATE TABLE Orders ( O_ID int NOT NULL, ORDER_NO int NOT NULL, C_ID int, PRIMARY KEY (O_ID), FOREIGN KEY (C_ID) REFERENCES Customers(C_ID) ) |
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