How to select 2 fields in where clause
You want to write this - which is valid SQL by the way - just not implemented in Sybase:

select *
from A
where (x,y) in (select u,v from B) ;


The easiest way is to rewrite is by using an EXISTS correlated subquery instead:

select * 
from A 
where exists
      (select 1 from B
       where A.x = B.u
         and A.y = B.v
      ) ;