use Modern::Perl;
use DBI;
use Data::Dumper;

my $dbh = DBI->connect('dbi:ODBC:DSN=myDSN', undef, undef, {RaiseError
+ => 1});
$dbh->{LongReadLen} = 1000000; 
$dbh->{LongTruncOk} = 1;


my $sth = $dbh->prepare(q{select * from table});
$sth->execute;

while (my $row = $sth->fetchall_arrayref) {
    say Dumper $row;
}
[download]

What I get is the following line repeated hundreds of times to STDERR

DBD::ODBC::st fetchall_arrayref warning: no select statement currently
+ executing
 at conn.pl line 17.
[download]

The code you are showing us is not the code you are running. You posted only 15 lines, so there is no line 17.

Show the code that is really running. If it is to long (more than about 30 lines), copy it, shorten it to the relevant parts, run it. Post the shortened code and the error messages and warnings it generates.

Alexander