Entity integrity

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In the relational data model, entity integrity is one of the three inherent integrity rules. Entity integrity is an integrity rule which states that every table must have a primary key and that the column or columns chosen to be the primary key should be unique and not NULL.[1]

Within relational databases using SQL, entity integrity is enforced by adding a primary key clause to a schema definition. The system enforces Entity Integrity by not allowing operation (INSERT, UPDATE) to produce an invalid primary key. Any operation that is likely to create a duplicate primary key or one containing nulls is rejected. The Entity Integrity ensures that the data that you store remains in the proper format as well as comprehensible.

See also[edit]


  1. ^ Beynon-Davies P. (2004). Database Systems 3rd Edition. Palgrave, Basingstoke, UK. ISBN 1-4039-1601-2