Re: EquivalenceClasses and subqueries and PlaceHolderVars, oh my

On 2012-03-15 02:29, Tom Lane wrote:>> explain select * from>  (select thousand as t1, tenthous as t2 from tenk1 a>
unionall>   select 42 as t1, 42 as t2 from tenk1 b) c> order by t1, t2;>> There is an EquivalenceClass for each of "t1"
and"t2", and if we don't> do something like wrapping the constants with distinct PHVs, then> add_child_rel_equivalences
willend up pushing identical constants into> both ECs, thus totally bollixing the fundamental rule that any expression>
shouldmatch at most one EC.
 

I'm having a hard time imagining that add_child_rel_equivalences is not 
just plain wrong. Even though it will only add child equivalence members 
to a parent eq class when certain conditions are met, isn't it the case 
that since a union (all) is addition of tuples and not joining, any kind 
of propagating restrictions on a append rel child member to other areas 
of the plan can cause unwanted results, like the ones currently seen?

regards,
Yeb Havinga