Re: limit clause breaks query planner?

"Tom Lane" <tgl@sss.pgh.pa.us> writes:
> I'm not sure offhand whether the existing correlation stats would be of use for
> it, or whether we'd have to get ANALYZE to gather additional data.

Please forgive the tangent, but would it be practical to add support for gathering statistics on an arbitrary
expressionassociated with a table, rather than just on materialized columns?  For example: 
    analyze my_tab for expression 'my_func(my_tab.col)' ;
It seems like any time you'd consider using a functional index, this feature would let the planner calculate decent
selectivityestimates for the expression's otherwise opaque data distribution.  The expression might be treated as a
virtualcolumn on the table; not sure if that helps or hurts.  Should I post this question on pgsql-hackers?