Re: [HACKERS] path toward faster partition pruning

Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> Amit Langote wrote:
>> [Jesper] also pointed out a case with a
>> list-partitioned table where pruning doesn't a produce a result as one
>> would expect and what constraint exclusion would produce.
>>
>> create table lp (a char) partition by list (a);
>> create table lp_ad partition of lp for values in ('a', 'd');
>> create table lp_bc partition of lp for values in ('b', 'c');
>> create table lp_default partition of lp default;
>> explain (costs off) select * from lp where a > 'a' and a < 'd';
>> QUERY PLAN
>> -----------------------------------------------------------
>> Append
>> -> Seq Scan on lp_ad
>> Filter: ((a > 'a'::bpchar) AND (a < 'd'::bpchar))
>> -> Seq Scan on lp_bc
>> Filter: ((a > 'a'::bpchar) AND (a < 'd'::bpchar))
>> -> Seq Scan on lp_default
>> Filter: ((a > 'a'::bpchar) AND (a < 'd'::bpchar))
>> (7 rows)
>>
>> One would expect that lp_ad is not scanned.

> One would? I, for one, wouldn't particularly sweat over this case TBH.

That example works in HEAD, so if somebody is proposing a patch that
breaks it, seems like that needs investigation.

regards, tom lane