Re: subquery abnormal behavior

Oh that explains a lot...

Thank you,
-------------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 12/11/06, Michael Glaesemann <grzm(at)seespotcode(dot)net> wrote:
>
>
> On Dec 11, 2006, at 15:48 , Shoaib Mir wrote:
>
> > create table myt1 (a numeric);
> > create table myt2 (b numeric);
> >
> > select a from myt1 where a in (select a from myt2);
> >
> > This should be giving an error that column 'a' does not exist in
> > myt2 but it runs with any error...
>
> The a in the IN clause is the same a in outer expression. This is in
> effect:
>
> select a from myt1 where a = a;
>
> Now, if you were to say
>
> select a from myt1 where a in (select myt2.a from myt2);
> ERROR: column myt2.a does not exist
> LINE 1: select a from myt1 where a in (select myt2.a from myt2);
>
> And if you were to instead have
> create table myt1 (a numeric);
> CREATE TABLE
> create table myt2 (b numeric);
> CREATE TABLE
> insert into myt1(a) values (1), (2);
> INSERT 0 2
> insert into myt2 (b) values (3), (4), (2);
> INSERT 0 3
> create table myt3 (a numeric);
> CREATE TABLE
> insert into myt3 (a) values (2), (3),(4);
> INSERT 0 3
> test=# select a from myt1 where a in (select a from myt3);
> a
> ---
> 2
> (1 row)
>
> It looks like PostgreSQL treats it as a natural join like
>
> select a from myt1 natural join myt3;
>
> Hope this helps.
>
> Michael Glaesemann
> grzm seespotcode net
>
>
>