how to query the sharepoint list with using lookup column

hi,

I have requrement like below

 List A

Title                         Postionid(Lookup)       PositionDescription

xxx@gmail.com             1                               xxxx

yyy@gmail.com             1                                xxx

pp@hotmail.com           1                                 xxx

sss@s.com                    2                                sss

eee@gmail.com             2                                www

List B

Title                         fistname  lastname age fathername

xxx@gmail.com         x             x             10      y

yyy@gmail.com         p            p               12      p

bbb@b.com               q           q                12     y

 here in List A positionid is lookup column i have creating one visual web part i am querying the List A using  query string as Positionid in that web part .finally what i want is i need date from list B on basis of corresponding position id here List A Title and List B title are same i need each candidate info how can i do it

Srinivas