Uhh .. errr ... uhhh ... check for return values and do what you need to? Basically, you're doing a bunch of stuff without checking return values. Also, you have RaiseError set on one of your connects so you could wrap the code inside an eval.

my $dbh = DBI->connect( $dsn, $user, $password,
                                     { RaiseError => 1 } );

if( ! $dbh ) {
    print "Ugg, connection problem: $DBI::errstr\n";
} else {
     eval {
          $dbh->do( whatever );
          $dbh->do( something else );
    };
 
    if( $@ ) {
        print "Ugg, problem: $@\n";
    }
}
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