Re: UNION ALL has higher cost than inheritance

Itagaki Takahiro <itagaki.takahiro@gmail.com> writes:
> On Thu, Oct 21, 2010 at 2:18 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> The plan for UNION initially involves a couple of SubqueryScan nodes,
>> which impose an extra cost of cpu_tuple_cost per tuple.  Those later
>> get optimized away, but we don't try to readjust the cost estimates
>> for that.

> Thanks. It also explains my another question why Merge Append cannot
> be used for UNION ALL plans.

Hmm, seems like the example you show ought to work.  I wonder if there
was an oversight in that patch...
        regards, tom lane