问在PostgreSQL中UNION之后是否保留了订单？

EN

CREATE TABLE audit_trail (
      old_email TEXT NOT NULL,
      new_email TEXT NOT NULL
);

INSERT INTO audit_trail(old_email, new_email)
  VALUES ('harold_gim@yahoo.com', 'hgimenez@hotmail.com'),
         ('hgimenez@hotmail.com', 'harold.gimenez@gmail.com'),
         ('harold.gimenez@gmail.com', 'harold@heroku.com'),
         ('foo@bar.com', 'bar@baz.com'),
         ('bar@baz.com', 'barbaz@gmail.com');


WITH RECURSIVE all_emails AS (
  SELECT  old_email, new_email
    FROM audit_trail
    WHERE old_email = 'harold_gim@yahoo.com'
  UNION
  SELECT at.old_email, at.new_email
    FROM audit_trail at
    JOIN all_emails a
      ON (at.old_email = a.new_email)
)
SELECT * FROM all_emails;

        old_email         |        new_email
--------------------------+--------------------------
 harold_gim@yahoo.com     | hgimenez@hotmail.com
 hgimenez@hotmail.com     | harold.gimenez@gmail.com
 harold.gimenez@gmail.com | harold@heroku.com
(3 rows)

select old_email, new_email into iter1
from audit_trail where old_email = 'harold_gim@yahoo.com';
select * from iter1;
--       old_email       |      new_email
-- ----------------------+----------------------
--  harold_gim@yahoo.com | hgimenez@hotmail.com
-- (1 row)

select a.old_email, a.new_email into iter2
from audit_trail a join iter1 b on (a.old_email = b.new_email);
select * from iter2;
--       old_email       |        new_email
-- ----------------------+--------------------------
--  hgimenez@hotmail.com | harold.gimenez@gmail.com
-- (1 row)

select * from iter1 union select * from iter2;
--       old_email       |        new_email
-- ----------------------+--------------------------
--  hgimenez@hotmail.com | harold.gimenez@gmail.com
--  harold_gim@yahoo.com | hgimenez@hotmail.com
-- (2 rows)