i guess u will hv to use cursor like this:
declare cursor c1 is
select cola ,colb from table2;
v_cola t2.cola%type;
v_colb t2.colb%type;
begin
open c1;
loop
fetch c1 into v_cola,v_colb;
exit when c1%notfound;
update table1
set colb = v_colb
where cola = v_cola;
end loop;
end c1;
end;
/
once u verify that values are ok issue a commit;

HTH