Very sorry for the trash..
===
Now I found a comment at just where I patched,
> * XXX if the typinput function is not immutable, we really ought to
> * postpone evaluation of the function call until runtime. But there
> * is no way to represent a typinput function call as an expression
> * tree, because C-string values are not Datums. (XXX This *is*
> * possible as of 7.3, do we want to do it?)
- Is it OK to *now* we can do this?
+ Is it OK to regard that we can do this *now*?
regards,
> Hello, I think this is a bug.
>
> The core of this problem is that coerce_type() fails for Var of
> type UNKNOWNOID.
>
> The comment for the function says that,
>
> > * The caller should already have determined that the coercion is possible;
> > * see can_coerce_type.
>
> But can_coerce_type() should say it's possible to convert from
> unknown to any type as it doesn't see the target node type. I
> think this as an inconsistency between can_coerce_type and
> coerce_type. So making this consistent would be right way.
>
> Concerning only this issue, putting on-the-fly conversion for
> unkown nonconstant as attached patch worked for me. I'm not so
> confident on this, though..
>
> regards,
>
> At Wed, 22 Apr 2015 23:26:43 -0700, Jeff Davis <pgsql@j-davis.com> wrote in <1429770403.4604.22.camel@jeff-desktop>
> > On Wed, 2015-04-22 at 20:35 -0700, David G. Johnston wrote:
> >
> > > But the fact that column "b" has the data type "unknown" is only a
> > > warning - not an error.
> > >
> > I get an error:
> >
> > postgres=# SELECT ' '::text = 'a';
> > ?column?
> > ----------
> > f
> > (1 row)
> >
> > postgres=# SELECT a=b FROM (SELECT ''::text, ' ') x(a,b);
> > ERROR: failed to find conversion function from unknown to text