<form action="" method="post">
   <input type="text" class="form-control" placeholder="Cari data bersadarkan ID">
   <input type="submit" name="cari" value="Cari" class="btn" style="padding:3px;" margin="6px;" width="50px;"  />
  </form
  <?php

   $input_cari = @$_POST['input_cari'];
   $cari = @$_POST['cari'];

   // jika tombol cari di klik
   if($cari) {

    // jika kotak pencarian tidak sama dengan kosong
    if($input_cari != "") {
    // query mysql untuk mencari berdasarkan nama negara. .
    $sql = mysql_query("select * from countries where country_name like '%$input_cari%'") or die (mysql_error());
    } else {
    $sql = mysql_query("select * from countries") or die (mysql_error());
    }
    } else {
    $sql = mysql_query("select * from countries") or die (mysql_error());
    }