use Data::Dumper;
my $placeHolder1 = 20;
my $sql = 'SELECT *.... where blablabla = ?';

my $sth = $dbh->prepare( $sql )
 or die "Error in preparing SQL: $DBI::errstr\nSQL: $sql\n\n";
$sth->execute( $placeHolder1 )
 or die "Error in executing SQL: ", $sth->errstr, "\n";

while( my $data = $sth->fetchrow_hashref ) {
  print Dumper( $data );
} # while
$sth->finish;