Re: Getting rid of SQLValueFunction

On Wed, Oct 19, 2022 at 03:45:48PM +0900, Michael Paquier wrote:
> With this in mind, would somebody complain if I commit that?  That's a
> nice reduction in code, while completing the work done in 40c24bf:
>  25 files changed, 338 insertions(+), 477 deletions(-)

On second look, there is something I have underestimated here with
FigureColnameInternal().  This function would create an attribute name
based on the SQL keyword given in input.  For example, on HEAD we
would get that:
=# SELECT * FROM CURRENT_CATALOG;
 current_catalog 
-----------------
 postgres
(1 row)

But the patch enforces the attribute name to be the underlying
function name, switching the previous "current_catalog" to
"current_database".  For example:
=# SELECT * FROM CURRENT_CATALOG;
 current_database 
------------------
 postgres
(1 row)

I am not sure how much it matters in practice, but this could break
some queries.  One way to tackle that is to extend
FigureColnameInternal() so as we use a compatible name when the node
is a T_FuncCall, but that won't be entirely water-proof as long as
there is not a one-one mapping between the SQL keywords and the
underlying function names, aka we would need a current_catalog.
"user" would be also too generic as a catalog function name, so we
should name its proc entry to a pg_user anyway, requiring a shortcut
in FigureColnameInternal().  Or perhaps I am worrying too much and
keeping the code simpler is better?  Does the SQL specification
require that the attribute name has to match its SQL keyword when
specified in a FROM clause when there is no aliases?

Thoughts?
--
Michael