ENABLE VALIDATE

specifies that all old and new data also complies with the
constraint. An enabled validated constraint guarantees that all data is and will
continue to be valid.

If any row in the table violates the integrity constraint, the constraint remains
disabled and Oracle returns an error. If all rows comply with the constraint, Oracle
enables the constraint. Subsequently, if new data violates the constraint, Oracle
does not execute the statement and returns an error indicating the integrity
constraint violation.

If you place a primary key constraint in ENABLE VALIDATE mode, the validation
process will verify that the primary key columns contain no nulls. To avoid this
overhead, mark each column in the primary key NOT NULL before entering data
into the column and before enabling the primary key constraint of the table.

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