delete 记录的问题?

Question

DECLARE
    v_NumCredits  classes.num_credits%TYPE;   CURSOR c_RegisteredStudents IS
    SELECT *
      FROM students
      WHERE id IN (SELECT student_id
                     FROM registered_students
                     WHERE department= 'HIS'
                     AND course = 101)
      FOR UPDATE OF current_credits;BEGIN
    FOR v_StudentInfo IN c_RegisteredStudents LOOP
 
  SELECT num_credits
    INTO v_NumCredits
    FROM classes
    WHERE department = 'HIS'
    AND course = 101;  UPDATE students
    SET current_credits = current_credits + v_NumCredits
    WHERE CURRENT OF c_RegisteredStudents;
  END LOOP;   COMMIT;
END;该update语句只更新在游标声明部分的for update子句中列出的列.如果没有列列出，则任一列都被更新.