RE: IN ignore null values

From: Mercadante, Thomas F <thomas.mercadante_at_labor.state.ny.us>
Date: Fri, 20 Feb 2004 09:47:41 -0500
Message-ID: <DE8A21F8F1D0254EA4A9214D52AB2FEDAD590A@exchsen0a1ma>

Juan,

Your queries really don't prove anything.

select null from daz.utl_tablas_me works the same as select 42 from daz.utl_tablas_me

Your use of the IN clause versus the EXISTS clause are different. The IN clause is comparing the tsm_dsm column against a value of NULL which should *never* return a true condition.

Your use of EXISTS says to return a TRUE value from the subquery if the query is valid. Performing a select null from table *always* returns a true result because you are not using a where clause.

Hope this helps.

Tom Mercadante
Oracle Certified Professional

-----Original Message-----

From: Juan Cachito Reyes Pacheco [mailto:jreyes_at_dazasoftware.com] Sent: Friday, February 20, 2004 9:33 AM
To: antonio; carlos; daniel; danita; ivan; jaime; javier; juan; luis; oracle-l_at_freelists.org; richi
Subject: IN ignore null values

An interesting observation

IN ignore null values as you can see in the table there are 310 null values in column TBL_DSM.

SQL> select count(*) from daz.utl_tablas_me

  2 where tbl_dsm in

  3 (select null from daz.utl_tablas_me);

 COUNT(*)

---

        0

SQL> select count(*) from daz.utl_tablas_me

  2 where exists(select null from daz.utl_tablas_me);

 COUNT(*)

---

      310

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Received on Fri Feb 20 2004 - 08:47:41 CST