Oracle ADD_MONTHS Test(01)

DECLARE

  M_DATE1    DATE;
  M_VARCHAR2 VARCHAR2(30) := '5';

  M_INTO1 VARCHAR2(50);
  M_INTO2 VARCHAR2(50);
  M_INTO3 VARCHAR2(50);
  M_INTO4 VARCHAR2(50);
  M_INTO5 VARCHAR2(50);

  --  
  M_INTO6 VARCHAR2(50);
  M_INTO7 VARCHAR2(50);
  M_INTO8 VARCHAR2(50);
BEGIN

  SELECT ADD_MONTHS(DATE '2015-01-01', -2) INTO M_DATE1 FROM DUAL;

  DBMS_OUTPUT.put_line(TO_CHAR(M_DATE1, 'YYYY-MM-DD'));

  --SELECT ADD_MONTHS((M_DATE1 + M_VARCHAR2 - 1), -1) INTO M_INTO1 FROM DUAL;  
  SELECT TO_CHAR(ADD_MONTHS((M_DATE1 + M_VARCHAR2 - 1), -1), 'YYYY-MM-DD')
    INTO M_INTO1
    FROM DUAL;

  DBMS_OUTPUT.put_line(M_INTO1);

  IF TO_NUMBER(TO_CHAR(SYSDATE, 'DD')) = 19 THEN
    DBMS_OUTPUT.put_line('1号');
  END IF;

  SELECT TO_CHAR(SYSDATE - 5, 'YYYY-MM-DD HH24:MM:SS')
    INTO M_INTO2
    FROM DUAL;
  SELECT TO_DATE('2014-06-10 12:05:22', 'YYYY-MM-DD HH24:MI:SS')
    INTO M_INTO3
    FROM DUAL;
  /*  SELECT TRUNC(ADD_MONTHS(SYSDATE, -1), 'MM') FIRST_DAY LAST_DAY(ADD_MONTHS(SYSDATE, -1)) LAST_DAY 
  FROM DUAL;*/

  -- SELECT TRUNC(ADD_MONTHS(SYSDATE, -1), 'MM') INTO M_INTO4 FROM DUAL;  

  -- SELECT LAST_DAY(ADD_MONTHS(SYSDATE, -1)) LAST_DAY INTO M_INTO5 FROM DUAL;  

  --上月第一天  
  SELECT TO_CHAR(TRUNC(ADD_MONTHS(SYSDATE, -1), 'MM'), 'YYYY-MM-DD')
    INTO M_INTO4
    FROM DUAL;
  --上月最后一天  
  SELECT TO_CHAR(LAST_DAY(ADD_MONTHS(SYSDATE, -1)), 'YYYY-MM-DD')
    INTO M_INTO5
    FROM DUAL;

  --本月第一天  
  SELECT TO_CHAR(TRUNC(ADD_MONTHS(SYSDATE, 0), 'MM'), 'YYYY-MM-DD')
    INTO M_INTO4
    FROM DUAL;

  --上一年的第一天   
  SELECT TO_CHAR(TRUNC(ADD_MONTHS(SYSDATE, -1), 'YY'), 'YYYY-MM-DD')
    INTO M_INTO4
    FROM DUAL;

  DBMS_OUTPUT.put_line(TRUNC(ADD_MONTHS(SYSDATE, -1), 'MM'));
  DBMS_OUTPUT.put_line(M_INTO4);
  DBMS_OUTPUT.put_line(M_INTO5);

  --加减时间练习  
  SELECT TO_CHAR(DATE '2015-01-01' - 1, 'YYYY-MM-DD')
    INTO M_INTO6
    FROM DUAL;
  SELECT TO_CHAR(TO_DATE('2015-02-01 15:14:21', 'yyyy-MM-dd HH24:mi:ss') - 1,
                 'YYYY-MM-DD')
    INTO M_INTO7
    FROM DUAL;
  SELECT TO_CHAR(TO_DATE('2015-02-01 15:14:21', 'yyyy-MM-dd HH24:mi:ss') - 1,
                 'YYYY-MM-DD HH24:mi:ss')
    INTO M_INTO8
    FROM DUAL;

END;