How to fetch the value from DataBase by Comparing the Columns of two Tables?

alter   PROCEDURE [dbo].[FMS_findteacherbysubject]
@sub nvarchar(50)
as

begin
if not exists (select l.StaffName,l.TeachingSubject from LeaveDetails l,StaffDetails s where s.StaffName=l.StaffName)
 begin
select s.StaffName,s.Qualification,s.Experience from StaffDetails s
 where s.Subject='@sub'
 end
 end

StaffName  id Subject from      to
Ashraf Ali 1 Maths 2013-12-02   2013-12-20


</pre>

Table 2
        StaffName        Quali Exp     Subject 
8	Ashraf Ali	M-Tech	2Year	Maths	
9	Jawed	        BBA	1Year	Physics	
10	Amar	        BA	1Year	Physics	
11	Saurabh	       B-Tech	5Year	Maths	
7	Rohit Sharma	B-Tech	1Year	Biology	
</pre>