Re: DBD::Pg (version 3.16.3) returns EMPTY char columns as 'undef'

2023年4月25日(火) 21:42 Matthias Apitz <guru(at)unixarea(dot)de>:
>
>
> Hello,
>
> We're using the above DBD::Pg version on Linux together with PostgreSQL 15.1
> On fetch empty char columns are returned as (Perl) 'undef'
>
> while ( my @row_ary = $dba->FetchArray()) {
> foreach my $i (0..$#row_ary) {
> if ($row_ary[$i] eq undef) {
> print $row_ary[1] . "\n";
> next;
> }
> ...
> which later leads in our code to NULL values '\N' in the writing of a CSV-like export
> files. Ofc NULL values in the database are something else as '' char
> strings.
>
> How this must be distinguished with DBD::Pg?

"eq undef" looks very wrong there:

$ perl -e "printf(qq|%i\n|, '' eq undef);"
1
$ perl -e "printf(qq|%i\n|, defined '');"
1

You probably want "if (!defined $row_ary[$i])". And possibly warnings enabled:

$ perl -w -e "printf(qq|%i\n|, '' eq undef);"
Use of uninitialized value in string eq at -e line 1.
1
$ perl -w -e "printf(qq|%i\n|, defined '');"
1

Regards

Ian Barwick