PL/SQL :: How To Get All Records Using CASE Function

first_tbl

First_dt second_dt Item
01-JAN-09     01-JUL-09     item1
01-APR-09     01-DEC-09     item1
01-JUL-09     31-DEC-09     item1
15-DEC-09     10-MAY-10     item1
20-MAR-12     10-AUG-12     item2
31-JUL-12     15-DEC-12     item2
01-APR-09     31-DEC-09     item2

second_tbl

Start_dt end_dt item flag
01-AUG-09     01-NOV-09 item1 null     
02-NOV-09     01-DEC-09     item1     null
01-DEC-09     15-DEC-09     item1     null
15-DEC-09     31-DEC-09 item1 null
01-JAN-10     10-MAY-10 item2 null
10-MAY-10     31-DEC-10     item2 null     
01-JAN-12     15-MAR-12     item2 null
20-MAR-12     31-JUL-12     item2 null

I need o/p in such a way that,if first_dt or second_dt in between start_dt and end_dt, i need to make the flag as y(item is the common join) other wise 'N'.

I was able to make the flag as'Y' but not 'N'

Select A.first_Dt, A.second_Dt, B.Start_Dt, B.End_Dt, A.item, B.item,

Case When B.falg is null
Then 'N'
Else 'Y'
End
From firsttbl A,second_tbl B
Where
A.item=B.item

and

((A.first_Dt>=B.Start_Dt And A.first_Dt<=B.End_Dt)          
Or     
(A.second_Dt>=B.Start_Dt And A.second_Dt<= B.End_Dt));