|
Posted by Justin Wyllie on November 24, 2004, 12:24 am
Please log in for more thread options
Hi
I have a problem with one line of code here:
$oldcount = $sth->fetchrow_array() or die("Error Number: 60");
The problem is that when the SQL, which just gets a one column one row value
has a value of 0 (zero) die is called - even though zero is a correct and
valid value. I suppose the zero is being evaluated as false.
My workaround is to get two columns from the SQL and throw away one and a
result set with two columns cannot be evaluated as false. But I wondered if
this was an inevitable result of using fetchrow_array in this way or whether
there is some other way round this
With regards
Justin Wyllie
|
|
Posted by Jim Gibson on November 23, 2004, 6:06 pm
Please log in for more thread options
> Hi
>
> I have a problem with one line of code here:
>
> $oldcount = $sth->fetchrow_array() or die("Error Number: 60");
>
> The problem is that when the SQL, which just gets a one column one row value
> has a value of 0 (zero) die is called - even though zero is a correct and
> valid value. I suppose the zero is being evaluated as false.
>
> My workaround is to get two columns from the SQL and throw away one and a
> result set with two columns cannot be evaluated as false. But I wondered if
> this was an inevitable result of using fetchrow_array in this way or whether
> there is some other way round this
According to the documentation (see 'perldoc DBI'), fetchrow_array()
returns an empty list if there are no rows or an error occurs. Although
a single column value in the row may be zero, you should still get the
number of columns in $oldcount, which should be 1 or more.
However, if returning no rows is not an error, you should not die based
on the return value from fetchrow_array(). Do what the documentation
says instead: check the value of $sth-err or use the RaiseError
attribute.
Also heed the warnings in the documentation about calling
fetchrow_array() in a scalar context. Maybe you should use (untested)
my @oldrow = $sth->fetch_array();
die $sth->errstr if $sth->err;
my $oldcount = @oldrow;
instead.
|
|
Posted by Justin Wyllie on November 24, 2004, 5:33 pm
Please log in for more thread options >
> > Hi
> >
> > I have a problem with one line of code here:
> >
> > $oldcount = $sth->fetchrow_array() or die("Error Number: 60");
> >
> > The problem is that when the SQL, which just gets a one column one row
value
> > has a value of 0 (zero) die is called - even though zero is a correct
and
> > valid value. I suppose the zero is being evaluated as false.
> >
> > My workaround is to get two columns from the SQL and throw away one and
a
> > result set with two columns cannot be evaluated as false. But I wondered
if
> > this was an inevitable result of using fetchrow_array in this way or
whether
> > there is some other way round this
>
> According to the documentation (see 'perldoc DBI'), fetchrow_array()
> returns an empty list if there are no rows or an error occurs. Although
> a single column value in the row may be zero, you should still get the
> number of columns in $oldcount, which should be 1 or more.
>
> However, if returning no rows is not an error, you should not die based
> on the return value from fetchrow_array(). Do what the documentation
> says instead: check the value of $sth-err or use the RaiseError
> attribute.
>
> Also heed the warnings in the documentation about calling
> fetchrow_array() in a scalar context. Maybe you should use (untested)
>
> my @oldrow = $sth->fetch_array();
> die $sth->errstr if $sth->err;
> my $oldcount = @oldrow;
>
> instead.
Hello Jim
Thanks. That was very illuminating.
$oldcount = $sth->fetchrow_array();
die $sth->errstr if $sth->err;
works fine. The main thing is it was evaluating the return value of 0 as
false and calling die. This isn't explicitly mentioned in the doc which
talks about Perl not being able to distinguish between the undef of an error
or the undef of an empty row.
Regards
Justin Wyllie
|
| Similar Threads | Posted | | Problem with DBD-mysql | November 20, 2004, 2:34 am |
| problem installing DBD-mysql | January 10, 2005, 5:51 pm |
| DBI Mysql insert problem | October 12, 2007, 6:18 pm |
| Problem with set_sql in Class::DBI::Loader::mysql | March 22, 2006, 2:47 pm |
| Mysql-DBD Perl module Installation Problem in HPUX | June 30, 2005, 9:05 am |
| [RESOLVED] DBD::mysql unresolved symbol _intel_fast_memcpy & mysql-standard-5.0.22-linux-i686-icc-glibc23 | August 29, 2006, 6:33 pm |
| MySQL 5.0 and Perl DBD-MySQL | December 3, 2005, 1:10 am |
| Embedded mysql with DBD::mysql | July 30, 2008, 10:15 am |
| DBD:mysql doesn't read mysql option file /etc/my.cnf file | January 27, 2005, 11:19 pm |
| DBD::mysql and UTF-8 | August 13, 2005, 11:27 am |
|
XML Sitemap