取两个时间差之间的天数

#结果如果差的天数为整，则直接获取；如果是差值之间的天数后面还有时分秒则，天数加1

CREATE function  fn_dev_datetime(date1 datetime year to second,date2 datetime year to second)
returning integer;

DEFINE out_day INTEGER;

DEFINE t_day INTEGER;
DEFINE t_hour INTEGER;
DEFINE t_minute INTEGER;
DEFINE t_second INTEGER;
DEFINE t_sum    INTEGER;

LET t_day = to_number(substr(date1 - date2,1,9));
LET t_hour = to_number(substr(date1 - date2,11,2));
LET t_minute = to_number(substr(date1 - date2,14,2));
LET t_second = to_number(substr(date1 - date2,17,2));
LET t_sum    = t_hour + t_minute + t_second;

if t_sum > 0 then
   LET out_day = t_day+1;
else
 LET out_day = t_day;
end if;

RETURN out_day;
end function;