OCP 1Z0 051 170

170. Which two statements are true regarding the DELETE and TRUNCATE commands? (Choose two.)

A. DELETE can be used to remove only rows from only one table at a time.

B. DELETE can be used to remove only rows from multiple tables at a time.

C. DELETE can be used only on a table that is a parent of a referential integrity constraint.

D. DELETE can be used to remove data from specific columns as well as complete rows.

E. DELETE and TRUNCATE can be used on a table that is a parent of a referential integrity constraint

having ON DELETE rule .

A delete一次只能删一个表的数据，当然truncate也只能删一个表

A对B错

C delete只能删除有参照约束中的主表。这显然不对，要先删除子表才能删除主表。

SQL> alter table emp2 add constraints fk_deptno foreign key (deptno) references dept2(deptno);
Table altered

SQL> delete from dept2;
delete from dept2
ORA-02292: integrity constraint (TEST.FK_DEPTNO) violated - child record found

SQL> delete emp2;
14 rows deleted

SQL> delete from dept2;
4 rows deleted

D delete可以只删几列的数据，这当然不可能。

E 不对，delete 可以，truncate不行

SQL> create table dept2 as select * from dept;
Table created

SQL> create table emp2 as select * from emp;
Table created

SQL> alter table dept2 add constraints pk_dept primary key(deptno);
Table altered

SQL> alter table emp2 add constraints fk_deptno foreign key (deptno) references dept2(deptno) on delete cascade;
Table altered

SQL> truncate table dept2;
truncate table dept2
ORA-02266: unique/primary keys in table referenced by enabled foreign keys

SQL> delete dept2;
4 rows deleted

又是一个有误的题

Answer: AE