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Re: [HACKERS] Re: [QUESTIONS] Practical SQL Handbook - demo script for postgreSQL

From: dg(at)illustra(dot)com (David Gould)
To: lockhart(at)alumni(dot)caltech(dot)edu (Thomas G(dot) Lockhart)
Cc: bruce(at)cenderis(dot)demon(dot)co(dot)uk, scrappy(at)hub(dot)org, pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: [HACKERS] Re: [QUESTIONS] Practical SQL Handbook - demo script for postgreSQL
Date: 1998-04-28 05:49:33
Message-ID: 9804280549.AA17187@hawk.illustra.com (view raw or flat)
Thread:
Lists: pgsql-hackers
> > > Don't know how or if we want to proceed with a bare "NULL" clause.
> > > Should we bother with a special case of _only_ NULL in a
> > > declaration, as in Bruce's patch?
> > My patch is clearly wrong.  The NULL should be parallel to NOT NULL,
> > and ought just to be ignored (since NULL is the default).  I think
> > it's worth doing (as the book says, NULL may not be the default on
> > your system, and anyway, it's always better to specify just for
> > clarity).
> > I think explicitly specifying NULL is probably good practice, so it
> > should be supported.
> 
> Maybe (SQL92 is full of inconsistant/non-symmetric features), but you
> will need to figure out how to do it without shift/reduce conflicts in
> the grammar. The fact that they are there means that either it is
> impossible to unambiguously parse the allowed syntax, or that the
> grammar definition in the yacc language needs to be restructured a bit.
> It isn't obvious to me how to restructure for this case; I've fixed this
> kind of problem in other parts of the grammar and the tricks I used
> there don't look usable here.
> 
> I know it isn't helpful to always fall back on "big philosophy" when you
> are proposing a small fix/improvement, but we should think about how
> much clutter we want to put in to the grammar. The "bare NULL" is
> apparently _not_ SQL92 (it does not appear in the BNF definitions in my
> SQL book by Date).
> 
> I'd like us to think about limiting the extensions to SQL92 in favor of
> extending the grammar toward Postgres' OR features. Just a thought...
> 
>                           - Tom

I strongly agree. Particularly about not whacking at the grammar. Even
"standard" SQL is quite confusing when writing queries. What is being asked
for is not part of the standard, and more importantly does not add any
capability to the system. Any extensions need to be vary carefully thought
out, and even then avoided unless there is a _compelling_ reason for them.

The test I try to use is "could I explain this feature over the phone and 
and provide a consistant 'story' about why it works the way it does"? So
that the listener can cope with all the exceptions, limitations, side
effects, errors etc just by relying on the theory from the explanation?

Generally if a proposed extension fails this test it turns out to be either
unimportant, or conceptually flawed.

Remember, the standard already has enough ad-hack semantics and syntactic
sugar, we certainly don't need to add more.

-dg

David Gould            dg(at)illustra(dot)com           510.628.3783 or 510.305.9468 
Informix Software  (No, really)         300 Lakeside Drive  Oakland, CA 94612
"(Windows NT) version 5.0 will build on a proven system architecture
 and incorporate tens of thousands of bug fixes from version 4.0."
                 -- <http://www.microsoft.com/y2k.asp?A=7&B=5>

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