You can
also specify a particular index that will enforce a constraint when you define that
constraint.
All constraints can be either immediate or deferred. An immediate constraint is
enforced as soon as a write operation affects a constrained column in the table. A
deferred constraint is enforced when the SQL statement that caused the change in the
constrained column completes. Because a single SQL statement can affect several
rows, the choice between using a deferred constraint or an immediate constraint can
significantly affect how the integrity dictated by the constraint operates. Youcan
Triggers | 107
specify that an individual constraint is immediate or deferred, or you can set the timing
for all constraints in a single transaction.
Finally, you can temporarily suspend the enforcement of constraints for a particular
table. When youenable the operation of the constraint, youcan instruct Oracle to
validate all the data for the constraint or simply start applying the constraint to the
new data. When youadd a constraint to an existing table, youcan also specify
whether you want to check all the existing rows in the table.
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