Referential integrity is the concept of relationships between tables, based on the definition of a primary key and a foreign key. The concept states that a row cannot exist in a table with a non-null value for a referencing column if an equal value does not exist in a referenced column.
You can specify columns in a referencing table that are foreign keys for columns in a referenced table. You must define referenced columns as either primary key columns or unique columns.
Referential integrity prevents accidental database inconsistencies when you perform inserts, merges, updates, and deletes.