Oracle: Row sources for INDEX SCAN operations

create table tq84_lu (txt varchar2(10), num number);


create table tq84_data (
   id    number,
   val   number,
   --
   lu_x  number,
   lu_y  number,
   lu_z  number
);

create index tq84_lu_ix on tq84_data (
       lu_x,
       lu_y,
       lu_z
);


explain plan for
select
   val
from
   tq84_data
where
   lu_x = (select num from tq84_lu where txt = 'x') and
   lu_y = (select num from tq84_lu where txt = 'y') and
   lu_z = (select num from tq84_lu where txt = 'z');

select * from table(dbms_xplan.display(format=>'basic Predicate'));
--
-- ----------------------------------------------------------
-- | Id  | Operation                           | Name       |
-- ----------------------------------------------------------
-- |   0 | SELECT STATEMENT                    |            |
-- |   1 |  TABLE ACCESS BY INDEX ROWID BATCHED| TQ84_DATA  |
-- |*  2 |   INDEX RANGE SCAN                  | TQ84_LU_IX |
-- |*  3 |    TABLE ACCESS FULL                | TQ84_LU    |
-- |*  4 |    TABLE ACCESS FULL                | TQ84_LU    |
-- |*  5 |    TABLE ACCESS FULL                | TQ84_LU    |
-- ----------------------------------------------------------
--  
-- Predicate Information (identified by operation id):
-- ---------------------------------------------------
--  
--    2 - access("LU_X"= (SELECT "NUM" FROM "TQ84_LU" "TQ84_LU" WHERE 
--               "TXT"='x') AND "LU_Y"= (SELECT "NUM" FROM "TQ84_LU" "TQ84_LU" WHERE 
--               "TXT"='y') AND "LU_Z"= (SELECT "NUM" FROM "TQ84_LU" "TQ84_LU" WHERE 
--               "TXT"='z'))
--    3 - filter("TXT"='x')
--    4 - filter("TXT"='y')
--    5 - filter("TXT"='z')

drop table tq84_lu;
drop table tq84_data;