10.

Examine the following statement that is used to modify the constraint on the SALES table:

SQL> ALTER TABLE SALES MODIFY CONSTRAINT pk DISABLE VALIDATE;

Which three statements are true regarding the above command? (Choose three.)

A.The constraint remains valid.

B.The index on the constraint is dropped.

C.It allows the loading of data into the table using SQL *Loader.

D.New data conforms to the constraint, but existing data is not checked

E.It allows the data manipulation on the table using INSERT/UPDATE/DELETE SQL statements.

Answer: ABC

答案解析：

本题考的是表约束， 

DISABLE 和ENABLE 是针对新增的数据是否符合约束，NOVALIDATE 和VALIDATE是针对已经存在的数据是否符合约束。

? DISABLE NOVALIDATE

? DISABLE VALIDATE

? ENABLE NOVALIDATE

? ENABLE VALIDATE

--约束状态：
enable validate： 启用约束，默认就是validate，指
   校验表中已存在的数据以及以后要插入的数据
enable novalidate：启用约束，只校验以后要插入的数据
disable validate：禁止约束，表将不允许dml操作，工具导入数据可以
disable novalidate：禁止约束，默认就是novalidate
插入不合理数据
create table t06 (id number primary key,
name varchar2(20));

insert into t06 values(1,'a');
insert into t06 values(1,'b');

select * from user_constraints;
select * from user_indexes;

alter table t06 disable constraint SYS_C003795;
insert into t06 values(1,'a');
insert into t06 values(1,'b');
create index t06_idx on t06(id);
alter table t06 enable novalidate constraint SYS_C003795;
commit;