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/ocms-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
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