Re: IN subquery not using a hash

Paul Tillotson <spam1011@adelphia.net> writes:
> Tom Lane wrote:
>> Hardly likely, considering it's estimating only 296 rows in the subquery
>> output.  My bet is that you've chosen a datatype whose comparisons are
>> not hashable (like char(n)).  What is the datatype of parentid in these
>> tables, anyway?
>>
> I don't have access to the machine now, but my memory is that
> parent.parentid is numeric(10,2) and child.parentid is int.

Offhand I don't believe there are any hashable crosstype comparisons.
In this case the int is probably getting promoted to numeric, but I
think numeric comparison isn't hashable either (because for example
'0.0' = '0.000' but the internal representations are different).

            regards, tom lane