Entity Integrity Rule in RDBMS

For Entity Integrity Rule, each table has a Primary Key.

Primary Key cannot have NULL value.

<Student>

Above, you can see our primary key is Student_ID. We cannot consider Student_Awards as the primary key since not every student would have received the award.

Let us see another example −

<Employee>

In the above table, the Primary Key is Employee_ID

Let us now summarize the Entity Integrity Rule −

• Make sure that each tuple in a table is unique.
• Every table mush has a primary key, for example, Student_ID for a Student table.
• Every entity is unique.
• The relations Primary Key must have unique values for each row.
• Primary Key cannot have NULL value and must be unique.
• Example can be an Employee_ID cannot be null in an Employee table.