Re: Boolean partition constraint behaving strangely

Dominik Sander <depairet(at)gmail(dot)com> writes:
> I have an issue with a table partitioned by one boolean column. The
> query planner only seems to skip the non matching table if expired
> (the column I use for the partition) is true.

Hm, interesting case. The reason it's behaving asymmetrically is the
fix for this bug:
http://archives.postgresql.org/pgsql-sql/2008-01/msg00084.php

The planner forces expressions like "bool_var = true" into the
simpler forms "bool_var" or "NOT bool_var" so as to recognize
that these forms are equivalent. However, that means that your
"expired = false" case looks like the case that was removed as
incorrect, ie

+ * Unfortunately we *cannot* use
+ * NOT A R=> B if: B => A
+ * because this type of reasoning fails to prove that B doesn't yield NULL.

It strikes me though that we could make the more limited deduction
that NOT A refutes A itself. That would fix this case, and I think
it would cover all the cases that we would have recognized if we'd
left the clauses in boolean-comparison form.

I'll see about fixing this for the next updates.

regards, tom lane