Re: SQL state: 42P01

"David Monarchi" <david(dot)e(dot)monarchi(at)gmail(dot)com> writes:
> When I execute the following query,
> select A.domain_name_dom, A.word_wdl, A.count_ofi, A.total_quality_ofi,
> A.avg_quality_ofi
> from zzz_brand2domain_step2_bs2 as A join
> (select B.domain_ofi, B.word_ofi, B.count_ofi, B.total_quality_ofi,
> B.avg_quality_ofi
> from offpagedomainwordintersection_ofi as B
> where B.domain_ofi != A.domain_name_dom
> order by B.total_quality_ofi desc
> limit 1) as C
> on A.word_wdl = B.word_ofi;

> I receive this error message
> ERROR: invalid reference to FROM-clause entry for table "a"
> LINE 5: where B.domain_ofi != A.domain_name_dom
> ^
> HINT: There is an entry for table "a", but it cannot be referenced from
> this part of the query.

> I don't understand why I can't reference the respective tables in the
> queries.

Because a JOIN happens between two *independent* tables. The above
isn't well-defined.

regards, tom lane