Question

define (a) primary key (b) foreign key

Answer 1

(a) PRIMARY KEY
A primary key, also called a primarykeyword, is a key in a relational database that is unique for each record. It is a unique identifier, such as a driver license number, telephone number (including area code), or vehicle identification number (VIN). A relational database must always have one and only one primary key.

(b) FOREIGN KEY
A foreign key is a column or columns of data in one table that connects to theprimary key data in the original table.

To ensure the links between foreign key and primary key tables aren't broken, foreign key constraints can be created to prevent actions that would damage the links between tables and prevent erroneous data from being added to the foreign key column.