DISABLE implies NOVALIDATE, unless VALIDATE is specified. VALIDATE and NOVALIDATE do not have default implications for the ENABLE and DISABLE states. When a unique or primary key moves from the DISABLE state to the ENABLE state and there is no existing index, a unique index is created automatically. Similarly when a unique or primary key moves from ENABLE to DISABLE and it is enabled with a unique index, the unique index is dripped. when any constraint is moved from the NOVALIDATE state to the VALIDATE state, all data must be checked. However moving from VALIDATE to NOVALIDATE simply forgets that the data was ever checked. Moving a single constraints from the ENABLE NOVALIDATE state to the ENABLE VALIDATE state does not block reads, writes, or other DDL statements.03) Briefly describe what is constraint checking?