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Re: String Translation

From: elein <elein(at)varlena(dot)com>
To: David Wheeler <david(at)kineticode(dot)com>
Cc: sfpug(at)postgresql(dot)org
Subject: Re: String Translation
Date: 2003-10-16 17:30:57
Message-ID: (view raw, whole thread or download thread mbox)
Lists: sfpug
The basic SQL is this:

   update <table> 
   	set <column>=fixident(<column>) 
   	where <column> = <column>;

If the table were "contrib" and the column in question
was "email", do:

   update contrib set email=fixident(email) where email=email;

And where fixident(text) is the perl function

create or replace function fixident (text) 
returns text as
      my $data = $_[0];
      $data =~ y/a-z0-9/_/cs;
      return $data;
' language 'plperl';

This should be faster.  You don't need to fetch
the value of the keyname before hand.

On Wed, Oct 15, 2003 at 05:21:14PM -0700, David Wheeler wrote:
> Hi All,
> I have an upgrade script for the forthcoming version of Bricolage. It 
> has a function that looks like this:
> sub update_all {
>     my ($table) = @_;
>     my $get_name     = prepare("SELECT name FROM $table");
>     my $set_key_name = prepare("UPDATE $table SET key_name=? WHERE 
> name=?");
>     my $name;
>     execute($get_name);
>     bind_columns($get_name, \$name);
>     while (fetch($get_name)) {
>         my $key_name = lc($name);
>         $key_name =~ y/a-z0-9/_/cs;
>         execute($set_key_name, $key_name, $name);
>     }
> }
> Now, this is all well and good, except that it takes _forever_ to run! 
> I have it running now on a database with two tables to be updated, with 
> a total of 2213 rows, and it has been running for about 30 mins. And 
> yes, it's a fast server with a reasonably tuned database.
> Now, I could speed this up if it could just run in a single query, 
> rather than with a big select and 2213 UPDATEs. The trouble is, I don't 
> know of an SQL equivalent to y/a-z0-9/_/cs, which translates any non 
> alphanumeric characters to underscores. I see that there's a 
> substring() function that supports POSIX regular expressions, but that 
> doesn't do a substitution.
> So my question is, does anyone know of a way I could do this in the 
> database (and it is a one-time change [I hope!])? And if there is one, 
> will it be faster?
> Many TIA,
> David
> -- 
> David Wheeler                                     AIM: dwTheory
> david(at)kineticode(dot)com                              ICQ: 15726394
>                     Yahoo!: dew7e
>                                                Jabber: Theory(at)jabber(dot)org
> Kineticode. Setting knowledge in motion.[sm]

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