use DBI;
  my ($db_name,$host_name,$port,$db_user,$db_pass,) = @_;
  my $database = "DBI:mysql:$db_name:$host_name:$port";
  my $dbh = DBI->connect($database,$db_user,$db_pass);

  my ($table, $col, $value) = ('clients', 'client_id', $client_id);

  my $sql = "select * from $table";
  if( $value ){
    $sql .= " where $col = ?";
    push @bind, $value;
  }
  my $href = $dbh->selectall_hashref($sql, $col, {}, @bind);