UPDATE Rules

Assignment: Update values are assigned to columns in accordance with the storage assignment rules described in Assignments and comparisons.

Validity: Updates must obey the following rules. If they do not, or if any other errors occur during the execution of the UPDATE statement, no rows are updated.

Triggers: If the identified table or the base table of the identified view has an update trigger, the trigger is activated. A trigger might cause other statements to be executed or raise error conditions based on the updated values.

Referential Integrity: The value of the parent key in a parent row must not be changed.

If the update values produce a foreign key that is nonnull, the foreign key must be equal to some value of the parent key of the parent table of the relationship.

The referential constraints (other than a referential constraint with a RESTRICT delete rule) are effectively checked at the end of the statement. In the case of a multiple-row UPDATE, this would occur after all rows were updated.