Mysql function select into不能给变量赋值

我在myqsl的function中写了这么一句：
SELECT COUNT(*) into intWorkDays from bf_Calendar where date between CAST('2009-01-14 15:23:36' AS datetime) and CAST('2009-01-16 15:00:00' AS datetime) and workday='0';

可是我在下面调用intWorkDays 变量时，intWorkDays =0，并没有得到我想要的值

整个function的代码如下：
CREATE DEFINER=`root`@`localhost` FUNCTION `NewFunction`(Timefrom DateTime,TimeTo DateTime) RETURNS int(11)
BEGIN
  DECLARE  intWorkDays int;
  DECLARE  intMinutes int;
  DECLARE  WorkDay char(1);
  DECLARE  Time800 datetime;
  DECLARE  Time1200 datetime;
  DECLARE  Time1700 datetime;
  DECLARE  Time1300 datetime;
  DECLARE  TimefromDate dateTime;
  DECLARE  TimeToDate dateTime;
  DECLARE  TimefromTime dateTime;
  DECLARE  TimeToTime dateTime;
  DECLARE  AMMinues int;
  DECLARE  PMMinutes int ;
 
    set TimefromDate= cast( date(Timefrom) as datetime);
   
    set TimefromTime= from_UNIXTIME( UNIX_TIMESTAMP(Timefrom) - UNIX_TIMESTAMP(TimefromDate));
    set TimeToDate= cast( date(TimeTo) as datetime);
 
set TimeToTime=  from_UNIXTIME( UNIX_TIMESTAMP(TimeTo) - UNIX_TIMESTAMP(TimeT