SQL & PL/SQL

Hi ,

i am trying this code ..


SELECT DISTINCT papf.full_name
FROM per_all_people_f papf,
per_all_assignments_f pav,
per_grades_tl pgt,
hr_all_organization_units haou
WHERE papf.person_id = pav.person_id
AND pgt.grade_id = pav.grade_id
AND haou.organization_id = pav.organization_id
--and papf.person_id=ppa.person_id
--and ppa.ANALYSIS_CRITERIA_ID=pac.ANALYSIS_CRITERIA_ID
AND SYSDATE BETWEEN papf.effective_start_date
AND papf.effective_end_date
AND SYSDATE BETWEEN pav.effective_start_date
AND pav.effective_end_date

AND NVL (haou.NAME, 0) =
NVL (:search_blkorganization_item, NVL (haou.NAME, 0))
AND NVL (pgt.NAME, 0) BETWEEN NVL (:search_blkgrade_from_item,
pgt.NAME
)
AND NVL (:search_blkgrade_to_item,
pgt.NAME
)
AND NVL (papf.date_of_birth,'31-DEC-4712')
BETWEEN NVL (:search_blkdob_item,papf.date_of_birth)
AND NVL (:search_blkdob_item_to,papf.date_of_birth)


i am trying to make all parameters to optional..

while i tried the nvl logic to make the date_of_birth field as optional
its giving the inconsistent data type error .

i tried with to_date,'31-DEC-4712'also ...but its giving error

anybody can help me

Regards,
kumar