Entity integrity

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In a relational database, entity integrity is a property that ensures that no records are duplicated and that no attributes that make up the primary key are NULL. It is one of the properties necessary to ensure the consistency of the database.

The existence of the Primary Key is the core of the entity integrity. If you define a primary key for each entity, they follow the entity integrity rule.

Although most relational databases do not specifically dictate that a table needs to have a Primary Key, it is good practice to design a Primary Key for each table in the relational model. This mandates no NULL content, so that every row in a table must have a value that denotes the row as a unique element of the entity.

The system enforces Entity Integrity by not allowing operations (INSERT, UPDATE) to produce an invalid primary key. Any operation that creates a duplicate primary key or one containing nulls is rejected.

[edit] See also

• Relational Database Management System
• Structured Query Language (SQL)
• Referential integrity