SQL & PL/SQL :: Extract Absent Days From The Month

i need to find the number of days employee was absent for the month, we are maintaining a table of attendance , where the daily data of hours is captured, what i need now is to capture total number of days he was absent or not present.How can i get the sum of absent days per employee based on given month, as the difficulty is i have to consider 30 days as standard working days for the month , regardless of months having either 30 days (April,June,September,November),or 31(January,March,May,July,August,December) or 28(Consider leap year also february) days.For eg ,If he is absent for 31 days in december then it should consider only 30 days as absent or if he is absent for 28 days in february still it should consider 30 Days as absent.

create table ot_job_det (jt_txn varchar2(12),jt_no number,jt_dt date ,jt_emp_code varchar2(6),jt_duration number )
delete from ot_job_det

[Code].....

I managed to do this with the given query , but this will check only for 31 days and 30 how to consider the february month or any leap year.

SELECT JT_EMP_CODE,DECODE(SIGN(30-COUNT(JT_DT)),-1,30,30-COUNT(JT_DT)) a FROM
OT_JOB_DET WHERE
TO_CHAR(JT_DT,'YYYYMM')='201212'
GROUP BY JT_EMP_CODE;