OCP 1Z0 052 170

170. A constraint in a table is defined with the INITIALLY IMMEDIATE clause. You executed the ALTER

TABLE command with the ENABLE VALIDATE option to enable the constraint that was disabled.

What are the two effects of this command? (Choose two.)

A.It fails if any existing row violates the constraint.

B.It does not validate the existing data in the table.

C.It enables the constraint to be enforced at the end of each transaction.

D.It prevents insert, update, and delete operations on the table while the constraint is in the process of

being enabled.

Answer: AD

http://docs.oracle.com/cd/E11882_01/server.112/e41084/clauses002.htm#SQLRF52221

Restriction on [NOT] DEFERRABLE You cannot specify either of these parameters for a view constraint.

INITIALLY Clause The

INITIALLY

clause establishes the default checking behavior for constraints that are

DEFERRABLE

.
The

INITIALLY

setting can be overridden by a

SET

CONSTRAINT

(

S

) statement in a subsequent transaction.

Specify

INITIALLY

IMMEDIATE

to
indicate that Oracle should check this constraint at the end of each subsequent SQL statement. If you do not specify

INITIALLY

at all, then the default is

INITIALLY

IMMEDIATE

.
If you declare a new constraint

INITIALLY

IMMEDIATE

, then it must be valid at the time the

CREATE

TABLE

or

ALTER

TABLE

statement
is committed or the statement will fail.

Specify

INITIALLY

DEFERRED

to indicate that Oracle
should check this constraint at the end of subsequent transactions.

This clause is not valid if you have declared the constraint to be

NOT

DEFERRABLE

, because a

NOT

DEFERRABLE

constraint
is automatically

INITIALLY

IMMEDIATE

and cannot ever be

INITIALLY

DEFERRED

.

VALIDATE | NOVALIDATE The behavior of

VALIDATE

and

NOVALIDATE

always
depends on whether the constraint is enabled or disabled, either explicitly or by default. Therefore they are described in the context of "ENABLE
Clause" and "DISABLE Clause".

ENABLE Clause Specify

ENABLE

if you want the constraint
to be applied to the data in the table.

If you enable a unique or primary key constraint, and if no index exists on the key, then Oracle Database creates a unique index. Unless you specify

KEEP INDEX

when subsequently disabling the constraint, this index is dropped
and the database rebuilds the index every time the constraint is reenabled.

You can also avoid rebuilding the index and eliminate redundant indexes by creating new primary key and unique constraints initially disabled. Then create (or use existing) nonunique indexes to enforce the constraint. Oracle does not drop a nonunique index
when the constraint is disabled, so subsequent

ENABLE

operations are facilitated.

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, then the constraint remains disabled and Oracle returns an error. If all rows comply with the constraint, then Oracle enables the constraint. Subsequently,
if new data violates the constraint, then 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, then 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.

ENABLE

NOVALIDATE

ensures that all new DML operations
on the constrained data comply with the constraint. This clause does not ensure that existing data in the table complies with the constraint.

If you specify neither

VALIDATE

nor

NOVALIDATE

, then the default is

VALIDATE

.

If you change the state of any single constraint from

ENABLE

NOVALIDATE

to

ENABLE

VALIDATE

, then the operation can
be performed in parallel, and does not block reads, writes, or other DDL operations.