DECLARE
  I NUMBER := 1;
BEGIN
  --1、for循环 
  FOR I IN REVERSE 1 .. 10 LOOP
    --reverse 可控制倒序循环，从10开始，10、9、8 ...
    DBMS_OUTPUT.PUT_LINE(TO_CHAR(SYSDATE, 'mi:ss'));
    DBMS_OUTPUT.PUT_LINE(I);
  END LOOP;

  FOR I IN (SELECT * FROM USER_OBJECTS WHERE ROWNUM < 6) LOOP
    DBMS_OUTPUT.PUT_LINE(I.OBJECT_ID);
    DBMS_OUTPUT.PUT_LINE(TO_CHAR(SYSDATE, 'mi:ss'));
  END LOOP;
  --2、while循环
  WHILE I != 6 LOOP
    DBMS_OUTPUT.PUT_LINE(I);
    I := I + 1;
  END LOOP;
  --3、loop循环
  I := 1;
  LOOP
    EXIT WHEN I = 10;
    DBMS_OUTPUT.PUT_LINE(I);
    I := I + 1;
  END LOOP;
END;