Entity integrity rules in RDBMS

For entity integrity rules, each table has a primary key.

Primary keys cannot have NULL values.

##Student_IDStudent AwardStudent_Awards

Above, you can see that our primary key is

Student_ID . We cannot treat Student_Awards as a primary key because not every student will receive that award.

Let’s see another example -

##Employee_ID

Employee Name

Employee_Age

Employee Location

In the above table, the primary key is

Employee_IDNow let us summarize the entities Integrity rules -

ensure that every tuple in the table is unique.

• Each table has a primary key, such as
Student_ID
• of the Student table. Each entity is unique.
• The relational primary key of each row must have a unique value.
• Primary keys cannot have NULL values ​​and must be unique.
• An example could be Employee_ID
• in the Employee table cannot be empty.

The above is the detailed content of Entity integrity rules in RDBMS. For more information, please follow other related articles on the PHP Chinese website!