oracle 日期校验 （判断）

CREATE OR REPLACE FUNCTION IS_DATE(
    IN_DATE IN VARCHAR2)
  RETURN INTEGER
AS
  FLAG INTEGER;
  YER VARCHAR2(4);
  MON VARCHAR2(2);
  TOD VARCHAR2(2);
BEGIN
  IF INSTR(IN_DATE, '-', 1, 1)=0 AND LENGTH(IN_DATE)=8 THEN
    YER :=SUBSTR(IN_DATE,1,4);
    MON :=SUBSTR(IN_DATE,5,2);
    TOD :=SUBSTR(IN_DATE,7,2);
  ELSE
    IF INSTR(IN_DATE, '-', 1, 1)=5 AND LENGTH(IN_DATE)=10 THEN
      YER :=SUBSTR(IN_DATE,1,4);
      MON :=SUBSTR(IN_DATE,6,2);
      TOD :=SUBSTR(IN_DATE,9,2);
    ELSE
      RETURN -1;
    END IF;
  END IF;
  IF MON NOT IN ('01','02','03','04','05','06','07','08','09','10','11','12') THEN
    RETURN -2;
  END IF;
  IF MON IN ('01','03','05','07','08','10','12') AND (TOD>'31' OR TOD<'01') THEN
    RETURN -3;
  END IF;
  IF MON IN('04','06','09','11') AND (TOD>'30' OR TOD<'01') THEN
    RETURN -4;
  END IF;
  IF MON='02' AND ((MOD(YER,4)=0 AND MOD(YER,100)<>0 OR MOD(YER,400)=0)) AND (TOD>'29' OR TOD<'01') THEN
    RETURN -5;
  END IF;
  IF MON='02' AND ( TOD>'28' OR TOD<'01') THEN
    RETURN -6;
  END IF;
  RETURN 0;
END IS_DATE;