--查重
SELECT t.aa1,t.aa2,t.aa4,t.aa5,COUNT(*) FROM tb_a t
  GROUP BY t.aa1,t.aa2,t.aa4,t.aa5
  HAVING COUNT(*) > 1;

SELECT *
  FROM tb_a
 WHERE (aa1, aa2, aa4, aa5) IN
       (SELECT t.aa1, t.aa2, t.aa4, t.aa5
          FROM tb_a t
         GROUP BY t.aa1, t.aa2, t.aa4, t.aa5
        HAVING COUNT(*) > 1);

--剔重
UPDATE tb_a t
   SET del_flag = 1
 WHERE (t.aa1, t.aa2, nvl(t.aa4,0), nvl(t.aa5,0), ROWID) IN
       (SELECT t.aa1, t.aa2, nvl(t.aa4,0), nvl(t.aa5,0), MAX(ROWID)
          FROM tb_a t
         GROUP BY t.aa1, t.aa2, nvl(t.aa4,0), nvl(t.aa5,0));

--删重
DELETE FROM tb_a t
 WHERE (t.aa1, t.aa2, nvl(t.aa4,0), nvl(t.aa5,0), ROWID) NOT IN
       (SELECT t.aa1, t.aa2, nvl(t.aa4,0), nvl(t.aa5,0), MAX(ROWID)
          FROM tb_a t
         GROUP BY t.aa1, t.aa2, nvl(t.aa4,0), nvl(t.aa5,0));