Comments on: Unnesting disjunctive subqueries (with OR predicate)

By: Igor Usoltsev

Igor Usoltsev — Sat, 09 Jun 2012 14:40:01 +0000

Thanks Timur, very interesting and another MOS-documented solution - by disabling of any unnest operations:

11.2.0.3.@SQL> select *
  2    from t2
  3   where not exists
  4          (select 1
  5            from t1
  6           where (t1.y = t2.y)
  7              or (t1.x = t2.y))
  8  /
            or (t1.x = t2.y))
                *
ERROR at line 7:
ORA-01790: expression must have same datatype as corresponding expression


SQL> select *
  2    from t2
  3   where not exists
  4          (select /*+ NO_UNNEST*/ 1
  5            from t1
  6           where (t1.y = t2.y)
  7              or (t1.x = t2.y))
  8  /

no rows selected

By: Timur Akhmadeev

Timur Akhmadeev — Fri, 08 Jun 2012 09:48:33 +0000

Hi Narendra

thank you for your comment.
Well, RBO is already deprecated but it’s not always possible to get rid of it.

By: Narendra

Narendra — Fri, 08 Jun 2012 09:05:04 +0000

What’s in total:
Predicates order matters sometimes
The way a predicate is written matters sometimes
After so many years of “matured CBO”, this quote is not going to help the “deprecation” of RB, I guess.
BTW, nice post.