On Thu, Apr 20, 2017 at 3:43 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> jonathan vanasco <postg...@2xlp.com> writes: > > Can anyone explain to me why the following is valid (running 9.6) ? > > > SELECT foo_id > > FROM example_a__data > > WHERE foo_id IN (SELECT bar_id FROM example_a__rollup) > > ; > > Per the SQL standard, bar_id is interpreted as an "outer reference" > to example_a__data.bar_id. This trips people up all the time, but > (a) it's required by spec and (b) there are cases where it's really > hard to do what you want without an outer reference. > > Cautious SQL programmers qualify all references inside sub-selects > to avoid getting caught by this accidentally. > I added an FAQ entry to the wiki for this question: https://wiki.postgresql.org/wiki/FAQ#Why_doesn.27t_PostgreSQL_report_a_column_not_found_error_when_using_the_wrong_name_in_a_subquery.3F David J.
