Editing ACID (section)

=== Consistency ===
{{Main article|Consistency (database systems)}}
[[consistency (database systems)|Consistency]] ensures that a transaction can only bring the database from one consistent state to another, preserving database [[Invariant (computer science)|invariants]]: any data written to the database must be valid according to all defined rules, including [[Integrity constraints|constraints]], [[Cascading rollback|cascades]], [[Database trigger|triggers]], and any combination thereof. This prevents database corruption by an illegal transaction. An example of a database invariant is [[referential integrity]], which guarantees the [[Unique key|primary key]]–[[foreign key]] relationship.<ref name="Date2012">C. J. Date, "SQL and Relational Theory: How to Write Accurate SQL Code 2nd edition", ''O'reilly Media, Inc.'', 2012, p. 180.</ref>