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Re: :PgSQL: More Queestions

From: David Wheeler <david(at)wheeler(dot)net>
To: Tim Bunce <Tim(dot)Bunce(at)pobox(dot)com>
Cc: Jeff Urlwin <jurlwin(at)bellatlantic(dot)net>, dbi-dev(at)perl(dot)org,pgsql-interfaces(at)postgresql(dot)org
Subject: Re: :PgSQL: More Queestions
Date: 2002-11-21 06:30:00
Message-ID: A95C6280-FD1A-11D6-8943-0003931A964A@wheeler.net (view raw or flat)
Thread:
Lists: pgsql-interfaces
On Wednesday, November 20, 2002, at 06:53  AM, Tim Bunce wrote:

>> But if I change it (as I'm seriously considering, in light of
>> PostgreSQL 7.3's support for prepared statements), I'll probably do no
>> parsing for comments.
>
> I think that would be a bad move.

Yes, your last post makes very clear why. Thanks.

> If it's seen the start of a string ("..." or '...') then it just
> keeps copying the string till it finds the same type of quote
> character to mark the end of the string. The 'fiddly bit in the
> middle' is handling backslashes used to escape quote chars in the
> middle of the string:  "...\"..." and "...\\" (odd vs even number).

Seems rather opaque. Maybe I'm just reflecting my C-newbieness, but why 
wouldn't this work as well? Borrowing a bit from DBD::ODBC here (but 
allowing for both kinds of escaping of the quote characters):

         if (*src == '"' || *src == '\'') {
             if (!in_literal) {
                 literal_ch = *src;
                 in_literal = 1;
             } else {
                 if (*src == literal_ch && *(src-1) != '//'
                     && *(src-1) != literal_ch) {
                     in_literal = 0;
                 }
             }
         }

> ANSI standard doesn't use backslashes, it uses doubling: "...""..."

Yeah, as Rudy pointed out, however, PostgreSQL uses backslashes as well 
as doubling.

> Take a look at dbd_preparse in DBD::Oracle.

Will do, when I'm more awake again and find the tuits...

> There's also a preparse() in DBI.xs which was destined to become a
> standard service offered to drivers - but isn't quite ready yet.

Hrm, yes, that could be quite handy, since dbd_preparse() seems to be 
one of the more complex driver functions...

Regards,

David

-- 
David Wheeler                                     AIM: dwTheory
david(at)wheeler(dot)net                                 ICQ: 15726394
http://david.wheeler.net/                      Yahoo!: dew7e
                                                Jabber: Theory(at)jabber(dot)org


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