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.
All uniqueness checks are effectively made at the end of the statement. In the case of a multiple-row UPDATE of a column involved in a unique index or unique constraint, this would occur after all rows were updated.
All check constraints are effectively validated at the end of the statement. In the case of a multiple-row UPDATE, this would occur after all rows were 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.
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