oracle 自然周跨年度 一周分成两部分

CREATE OR REPLACE FUNCTION UDF_WEEKOFYEAR ( V_DATE IN date ,formate IN VARCHAR2 ) RETURN char
AS
v_ret char(6);
v_ret1 char(2);
v_ret3 NUMBER;
BEGIN

v_ret3 := TO_CHAR (v_date, 'iw');
IF v_ret3 = 1 AND TO_CHAR (v_date, 'mm') = '12' then --判断是否是最后一个月 周次算成下年了第一周

SELECT TO_CHAR(DECODE(SIGN((V_DATE
+TO_NUMBER(DECODE(TO_CHAR(TRUNC(V_DATE,'YYYY'),'D'),'1','8',
TO_CHAR(TRUNC(V_DATE,'YYYY'),'D'))) - 2)
-LAST_DAY(V_DATE)),1,LAST_DAY(V_DATE),
(V_DATE
+TO_NUMBER(DECODE(TO_CHAR(TRUNC(V_DATE,'YYYY'),'D'), '1','8',
TO_CHAR(TRUNC(V_DATE,'YYYY'),'D'))) - 2)),'WW') as week
into v_ret1 FROM DUAL;
return to_char(v_date,'yyyy')||v_ret1;
end if;

IF v_ret3 = 53 AND TO_CHAR (v_date, 'mm') = '01' then--判断是否是第一个月 周次算成去年了最后一周 那么拆分成两个周

SELECT TO_CHAR(DECODE(SIGN((V_DATE
+TO_NUMBER(DECODE(TO_CHAR(TRUNC(V_DATE,'YYYY'),'D'),'1','8',
TO_CHAR(TRUNC(V_DATE,'YYYY'),'D'))) - 2)
-LAST_DAY(V_DATE)),1,LAST_DAY(V_DATE),
(V_DATE
+TO_NUMBER(DECODE(TO_CHAR(TRUNC(V_DATE,'YYYY'),'D'), '1','8',
TO_CHAR(TRUNC(V_DATE,'YYYY'),'D'))) - 2)),'WW') as week
into v_ret1 FROM DUAL;
return to_char(v_date,'yyyy')||v_ret1;
end if;

if to_char(trunc(v_date,'yyyy'),'iw') = 53 and TO_CHAR (v_date, 'mm') = '01' then --判断是否是第一个月 周次算成去年了最后一周
v_ret := TO_CHAR (v_date, formate) + 1; --以后的周次向后推一
RETURN v_ret;
end if;

v_ret := TO_CHAR (v_date, formate); --正常情况下按自然周处理
RETURN v_ret;

END;