When we say a database has data integrity, we ensure that all tables in the database contain accurate and consistent data. For example, before we insert new data in CUSTOMER_ORDER table, we make sure the items to be ordered exist in PARTS table.

Constraint, also referred to integrity constraint, is an effective way to ensure data integrity in a relational database. There are several types of commonly used integrity constraints, including domain integrity such as not null and check constraints, as well as referential integrity. This discussion focuses on referential integrity.

 

1. What is a primary key?
2. What is a foreign key?
3. Why is a foreign key needed?

4. How to define a foreign key?
   

Please make sure to answer each of the question.

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