try this
create table tbl(
vendorid int,
clientid int)
insert into tbl values(100,1001)
insert into tbl values(100,1001)
insert into tbl values(100,1003)
insert into tbl values(200,1001)
insert into tbl values(200,1003)
insert into tbl values(300,1001)
insert into tbl values(300,1001)
insert into tbl values(300,2003)
select vendorID,clientid, dense_RANK() over(order by vendorID,clientid) from tbl
order by vendorID,clientid