-- 给个例子给你：

SET SERVEROUTPUT ON
DECLARE
  CURSOR c_student IS
    SELECT first_name, last_name, student_id
      FROM student
     WHERE last_name LIKE 'J%';
  CURSOR c_coruse (i_student_id IN student.student_id%TYPE) IS
    SELECT c.description, s.section_id sec_id
      FROM course c, section s, enrollment e
     WHERE e.student_id = i_studnet_id
       AND c.course_no = s.course_no
       AND s.section_id = e.section_id;
  COURSOR c_grade(i_section_id IN section.section_id%TYPE, i_student_id IN student.student_id%TYPE) IS
    SELECT gt.description grd_desc, TO_CHAR(AVG(g.numeric_grade), '999.99') num_grd
      FROM enrollment e, grade g, grade_type gt
     WHERE e.section_id = i_section_id
       AND e.student_id = g.student_id
       AND e.student_id = i_student_id
       AND e.section_id = g.section_id
       AND g.grade_type_code = gt.grade_type_code
     GROUP BY gt.description;
BEGIN
  FOR r_student IN c_student
  LOOP
    DBMS_OUTPUT.PUT_LINE(CHR(10));
    DBMS_OUTPUT.PUT_LINE(r_student.first_name||' '||r_student.last_name);
    FOR r_course IN c_course(r_student.student_id)
    LOOP
      DBMS_OUTPUT.PUT_LINE('Grades for course: '||r_course.description);
      FOR r_grade IN c_grade(r_course.sec_id, r_student.student_id)
      LOOP
        DBMS_OUTPUT.PUT_LINE(r_grade.num_grd||' '||r_grade.grd_desc);
      END LOOP;
    END LOOP;
  END LOOP;
END;
/

------解决方案--------------------
SQL code

--如果数据库对象作为变量，需要使用动态游标

declare 

v_tableName varchar2(20) := 'user_tables';
v_str varchar2(50);

type tcur is ref cursor; 
cur tcur;
begin
  

open cur  for 'select table_name from '||v_tableName;
loop
  fetch cur into v_str;
  exit when cur%notfound ;
  
  dbms_output.put_line(v_str);

end loop ;

close cur;
end ;