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Oracle SQL Plan operation MERGE JOIN (CARTESIAN)

The MERGE JOIN (CARTESIAN) execution plan operation always has two child row sources.

The second child row source is a BUFFER SORT operation.

drop table tq84_A;
drop table tq84_B;

begin
   dbms_random.seed(42);
end;
/

create table tq84_A as
select
   trunc(dbms_random.value(1, 50)) as nm,
   dbms_random.string('a', 20)     as tx
from
   dual connect by level <= 12;

create table tq84_B as
select
   trunc(dbms_random.value(1, 50)) as nm,
   dbms_random.string('a', 20)     as tx
from
   dual connect by level <=  7;
   
begin
   dbms_stats.gather_table_stats(user, 'tq84_A');
   dbms_stats.gather_table_stats(user, 'tq84_B');
end;
/

explain plan for
select
   a.nm  nm_a,
   b.nm  nm_b,
   a.tx  tx_a,
   b.tx  tx_b
from
   tq84_A a,
   tq84_B b
;
--
-- ---------------------------------------
-- | Id  | Operation            | Name   |
-- ---------------------------------------
-- |   0 | SELECT STATEMENT     |        |
-- |   1 |  MERGE JOIN CARTESIAN|        |
-- |   2 |   TABLE ACCESS FULL  | TQ84_B |
-- |   3 |   BUFFER SORT        |        |
-- |   4 |    TABLE ACCESS FULL | TQ84_A |
-- ---------------------------------------


select * from table(dbms_xplan.display(format=>'basic'));

Oracle SQL Plan operation MERGE JOIN (CARTESIAN)

See also