How can I display DB contents after selecting a dropdown list option using PHP, AJAX and MySQL?

I am new to AJAX and want to create something with two dropdown boxes. When a user selects the first one, the second dropdown populates with the corresponding fields. After selecting an option from the second dropdo开发者_开发百科wn I want a table to display all information from the database that corresponds to the selection. I have found an example online, but am having trouble modifying it. I am only able to display one field. This is the code:

ajax_select

//function used to remove the next lists already displayed when it chooses other options
    function removeLists(colid) {
  var z = 0;
  // removes data in elements with the id stored in the "ar_cols" variable
  // starting with the element with the id value passed in colid
  for(var i=1; i<ar_cols.length; i++) {
    if(ar_cols[i]==null) continue;
    if(ar_cols[i]==colid) z = 1;
    if(z==1) document.getElementById(preid+ar_cols[i]).innerHTML = '';
  }
}

// create the XMLHttpRequest object, according browser
function get_XmlHttp() {
  // create the variable that will contain the instance of the XMLHttpRequest object (initially with null value)
  var xmlHttp = null;

  if(window.XMLHttpRequest) { xmlHttp = new XMLHttpRequest(); }     // for Forefox, IE7+, Opera, Safari
  else if(window.ActiveXObject) { xmlHttp = new ActiveXObject("Microsoft.XMLHTTP"); }      // IE5 or 6

  return xmlHttp;
}

// sends data to a php file, via POST, and displays the received answer
function ajaxReq(col, wval) {
  removeLists(col);           // removes the already next selects displayed

  // if the value of wval is not '- - -' and '' (the first option)
  if(wval!='- - -' && wval!='') {
    var request =  get_XmlHttp();             // call the function with the XMLHttpRequest instance
    var php_file = 'select_list.php';     // path and name of the php file

    // create pairs index=value with data that must be sent to server
    var  data_send = 'col='+col+'&wval='+wval;

    request.open("POST", php_file, true);           // set the request

    document.getElementById(preid+col).innerHTML = 'Loadding...';   // display a loading notification

    // adds a header to tell the PHP script to recognize the data as is sent via POST
    request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    request.send(data_send);            // calls the send() method with data_send

    // Check request status
    // If the response is received completely, will be added into the tag with id value of "col"
    request.onreadystatechange = function() {
      if (request.readyState==4) {
        document.getElementById(preid+col).innerHTML = request.responseText;
      }
    }
  }
}

selected_list.php

    <?php
    // Multiple select lists - www.coursesweb.net/ajax/
    if(!isset($_SESSION)) session_start();

    // Here add your own data for connecting to MySQL database
    $server = 'localhost';
    $user = 'root';
    $pass = '***';
    $dbase = '**';

    // Here add the name of the table and columns that will be used for select lists, in their order
    // Add null for 'links' if you don`t want to display their data too
    $table = 'cpu_table';
    $ar_cols = array('endor', 'ype', 'name');

    $preid = 'slo_';        // a prefix used for element's ID, in which Ajax will add <select>
    $col = $ar_cols[0];     // the variable used for the column that wil be selected
    $re_html = '';          // will store the returned html code

    // if there is data sent via POST, with index 'col' and 'wval'
    if(isset($_POST['col']) && isset($_POST['wval'])) {
      // set the $col that will be selected and the value for WHERE (delete tags and external spaces in $_POST)
      $col = trim(strip_tags($_POST['col']));
      $wval = "'".trim(strip_tags($_POST['wval']))."'";
    }

    $key = array_search($col, $ar_cols);            // get the key associated with the value of $col in $ar_cols
    $wcol = $key===0 ? $col : $ar_cols[$key-1];     // gets the column for the WHERE clause
    $_SESSION['ar_cols'][$wcol] = isset($wval) ? $wval : $wcol;    // store in SESSION the column and its value for WHERE

    // gets the next element in $ar_cols (needed in the onchange() function in <select> tag)
    $last_key = count($ar_cols)-1;
    $next_col = $key<$last_key ? $ar_cols[$key+1] : '';

    $conn = new mysqli($server, $user, $pass, $dbase);     // connect to the MySQL database

    if (mysqli_connect_errno()) { exit('Connect failed: '. mysqli_connect_error()); }     // check connection

    // sets an array with data of the WHERE condition (column=value) for SELECT query
    for($i=1; $i<=$key; $i++) {
      $ar_where[] = '`'.$ar_cols[$i-1].'`='.$_SESSION['ar_cols'][$ar_cols[$i-1]];
    }

    // define a string with the WHERE condition, and then the SELECT query
    $where = isset($ar_where) ? ' WHERE '. implode($ar_where, ' AND ') : '';
    $sql = "SELECT DISTINCT `$col` FROM `$table`".$where;

    $result = $conn->query($sql);       // perform the query and store the result

    // if the $result contains at least one row
    if ($result->num_rows > 0) {
      // sets the "onchange" event, which is added in <select> tag
      $onchg = $next_col!==null ? " onchange=\"ajaxReq('$next_col', this.value);\"" : '';

      // sets the select tag list (and the first <option>), if it's not the last column
      if($col!=$ar_cols[$last_key]) $re_html = $col. ': <select name="'. $col. '"'. $onchg. '><option>- - -</option>';

      while($row = $result->fetch_assoc()) {
        // if its the last column, reurns its data, else, adds data in OPTION tags
        if($col==$ar_cols[$last_key]) $re_html .= '<br/>'. $row[$col];
        else $re_html .= '<option value="'. $row[$col]. '">'. $row[$col]. '</option>';
      }

      if($col!=$ar_cols[$last_key]) $re_html .= '</select> ';        // ends the Select list
    }
    else { $re_html = '0 results'; }

    $conn->close();

    // if the selected column, $col, is the first column in $ar_cols
    if($col==$ar_cols[0]) {
      // adds html code with SPAN (or DIV for last item) where Ajax will add the select dropdown lists
      // with ID in each SPAN, according to the columns added in $ar_cols
      for($i=1; $i<count($ar_cols); $i++) {
        if($ar_cols[$i]===null) continue;
        if($i==$last_key) $re_html .= '<div id="'. $preid.$ar_cols[$i]. '"> </div>';
        else $re_html .= '<span id="'. $preid.$ar_cols[$i]. '"> </span>';
      }

      // adds the columns in JS (used in removeLists() to remove the next displayed lists when makes other selects)
      $re_html .= '<script type="text/javascript">var ar_cols = '.json_encode($ar_cols).'; var preid = "'. $preid. '";</script>';
    }
    else echo $re_html;
    ?>

Is there an easier way to achieve this?

Thank You

This is what I use to get database content in a dropdownlist.

<?php 
mysql_connect('localhost','username','password');
mysql_select_db('databasename');
$query = mysql_query("SELECT columname FROM tablename");

echo '<select name="name">';
while ($row = mysql_fetch_array($query)) {
echo '<option value="'.$row['columname'].'">'.$row['columname'].'</option>';
}

echo '</select>';
?>

(I know mysql_ is not the way anymore but this worked for me) hopefully this works for you aswell