RE: Sarge problems with MySQL and DBI / DBD::mysql

["John Trammell" <johnt@holmescorp.com>]

#!perl

use strict;
use warnings;

sub foo {
    warn "wantarray() in foo() is: ", wantarray(), "\n";
    my @r = 3 .. 8;
    return @r;
}

my @x = foo() or warn "in ... or warn() #1\n";
warn "\@x: @x\n";

my $x = foo() or warn "in ... or warn() #2\n";
warn "\$x: $x\n"; 

> -----Original Message-----
> From: Michael Stassen [mailto:Michael.Stassen@verizon.net] 
> Sent: Tuesday, June 21, 2005 12:48 PM
> To: olly@lfix.co.uk
> Cc: debian-user@lists.debian.org; mysql@lists.mysql.com
> Subject: Re: Sarge problems with MySQL and DBI / DBD::mysql
> 
> Oliver Elphick wrote:
> 
> > We have an application that has just upgraded to Debian 
> sarge with mysql
> > upgrading from 3.23.49 to 4.0.24.  As far as I know I have 
> followed all
> > the procedures for upgrading the database.
> > 
> > Some queries always fail in DBD::mysql (in DBI) although 
> they work OK
> > with the mysql client.
> > 
> > For example, this SQL command:
> > 
> > 	SELECT description
> > 		FROM IncoCountry
> > 		WHERE value = "EW";
> > 
> > which returns 0 rows, works correctly in mysql.  But when 
> it is passed
> > through this statement in Perl:
> > 
> >         my @row = $dbh->selectrow_array($sql) or
> >                 &failed(__FILE__, __LINE__,
> >                  "Failed to run the sql statement with error
> >                   $DBI::errstr");
> > 
> > it fails inside DBD::mysql without giving any message in 
> $DBI::errstr:
> 
> This does not fail.  Your logic is wrong.  You are evaluating 
> $dbh->selectrow_array($sql) in a scalar context 
> (selectrow_array or ...). 
> According to `perldoc DBI`, in the section on 
> selectrow_array, "in a scalar 
> context, an "undef" is returned if there are no more rows".  
> Your query 
> successfully returns 0 rows, so $dbh->selectrow_array($sql) 
> is "undef".  undef 
> is false, so the part of your query after the "or" gets run.  
> You've coded an 
> error message which claims the query produced a DBI error, 
> but it did not.
> 
> > DBD::mysql::db::prepare(/usr/lib/perl5/DBD/mysql.pm:208):
> > 208:        my $sth = DBI::_new_sth($dbh, {'Statement' => 
> $statement});
> >   DB<2> n
> > DBD::mysql::db::prepare(/usr/lib/perl5/DBD/mysql.pm:211):
> > 211:        if (!DBD::mysql::st::_prepare($sth, $statement, 
> $attribs)) {
> >   DB<2> s
> > DBD::mysql::db::prepare(/usr/lib/perl5/DBD/mysql.pm:215):
> > 215:        $sth;
> >   DB<2> s
> > 
> main::failed(/home/domain/www.chpresenters.co.uk/web/cgi-bin/o
> cms-multi/common/cgi-lib.pl:117):
> > 
> > If a row is added to the table to be returned by this 
> query, the problem
> > goes away.
> > 
> > How can I debug or fix this problem, please?
> 
> You need to revise your code to distinguish between DBI 
> errors and 0 rows 
> returned.
> 
> Michael
> 
> -- 
> MySQL General Mailing List
> For list archives: http://lists.mysql.com/mysql
> To unsubscribe:    
> http://lists.mysql.com/mysql?unsub=johnt@holmescorp.com
> 
>