052-204(新增70题2018)

iew the Exhibit to see the structure of the EMPLOYEES and DEPARTMENTS tables.
Your organization plans to dissolve the department with department ID 30. You execute the following command to delete rows from the DEPARTMENTS table:
SQL> delete from DEPARTMENTS
where DEPT_ID = 30;
The command fails and displays the following error:
ERROR at line 1:
ORA-02292: integrity constraint (HR.SYS_C005374) violated - child record found
Which two actions would you take to overcome this error? (Choose two.)
Exhibit:

A. alter the foreign key constraint to include the cascade option

B. alter the foreign key constraint to include the on delete cascade option

C. first, drop the EMPLOYEES table and then delete the rows from the DEPARTMENTS table

D. first, drop the DEPARTMENTS table and then delete the rows from the EMPLOYEES table

E. first, delete all of the rows from EMPLOYEES table and then delete the rows from the DEPARTMENTS table for department id 30

F. first, delete rows from the EMPLOYEES table for department id 30 and then delete the rows from the DEPARTMENTS table for dep

Answer: BF
B是级联删除，F是删除指定关联数据

DELETE CASCADE Trigger for Parent Table

The trigger in Example 9-14 enforces the DELETE CASCADE referential action on the primary key of the dept table.

CREATE OR REPLACE TRIGGER dept_del_cascade
  AFTER DELETE ON dept
  FOR EACH ROW

  -- Before row is deleted from dept,
  -- delete all rows from emp table whose DEPTNO is same as
  -- DEPTNO being deleted from dept table:

BEGIN
  DELETE FROM emp
  WHERE emp.Deptno = :OLD.Deptno;
END;
/