PL/SQL :: Closest Date Missing Data

My requirement is to find the closest date from col B(a.p_date) to the dates in col A(d.p_date). I got the following which works great:

SELECT
d.p_no_s,
d.p_date,
MIN(a.p_date),
MIN(a.p_date)-d.p_date||' Number of Days' NUM_OF_DAYS

[Code]...

Output:

p_no_s p_date MIN(a.p_date) MIN(a.p_date)-d.p
-------------------- ---------- ---------- -------------------------------------------------------

Z1575560 15/06/2008 29/07/2008 44 Number of Days
Z1575560 15/07/2008 29/07/2008 14 Number of Days
Z1575560 21/11/2008 27/12/2008 36 Number of Days
Z1575560 17/12/2008 27/12/2008 10 Number of Days

Problem:

For 1st and 2nd row,

I am getting 29/07/2008 as a.p_date for both 15/06/2008 and 15/07/2008 which is wrong in my scenario. This is because data is missing in the second table for row 1 (similarly for row 3). So What I want is :

Z1575560 15/06/2008
Z1575560 15/07/2008 29/07/2008 14 Number of Days
Z1575560 21/11/2008
Z1575560 17/12/2008 27/12/2008 10 Number of Days

Say for eg: a person is in city A. He is departing on (15/06/2008 ) and arriving on 29/07/2008 and again departing on 15/07/2008 which is not possible.

It should be departing on (15/06/2008 ) and arriving between 15/06/2008 and 15/07/2008 (missing data hence null is required here) and departing on 15/07/2008 and arriving on 29/07/2008 .

let me know how to achieve this.