AJAX database

AJAX can be used to communicate interactively with a database.

AJAX Database Example

The following example will demonstrate how a web page reads information from the database through AJAX:

Example

Select the corresponding option, the user information will be displayed here...

Explanation of examples - MySQL database

In In the above example, the database table we use is as follows:

##2LoisGriffin40NewportPiano Teacher3JosephSwanson39QuahogPolice Officer4GlennQuagmire41QuahogPilot

id	FirstName	LastName	Age	Hometown	Job
1	Peter	Griffin	41	Quahog	Brewery

##Example explanation - HTML page

When the user is in When a user is selected in the drop-down list above, a function named "showUser()" will be executed. This function is triggered by the "onchange" event:

<html>
<head>
<script>
function showUser(str)
{
     if (str=="")
     {
           document.getElementById("txtHint").innerHTML="";
           return;
     } 
    if (window.XMLHttpRequest)
    {
           // IE7+, Firefox, Chrome, Opera, Safari 浏览器执行代码
           xmlhttp=new XMLHttpRequest();
     }
     else
     {
           // IE6, IE5 浏览器执行代码
           xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
     }
     xmlhttp.onreadystatechange=function()
     {
          if (xmlhttp.readyState==4 && xmlhttp.status==200)
          {
                document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
          }
     }
     xmlhttp.open("GET","getuser.php?q="+str,true);
     xmlhttp.send();
}
</script>
</head>
<body>
<form>
<select name="users" onchange="showUser(this.value)">
<option value="">Select a person:</option>
<option value="1">Peter Griffin</option>
<option value="2">Lois Griffin</option>
<option value="3">Glenn Quagmire</option>
<option value="4">Joseph Swanson</option>
</select>
</form>
<br>
<div id="txtHint"><b>Person info will be listed here.</b></div>
</body>
</html>

showUser() function performs the following steps:

PHP file

The server page called above through JavaScript is a PHP file named "getuser.php". The source code in

"getuser.php" runs a query against the MySQL database and returns the results in an HTML table:

<?php
$q=$_GET["q"];
$con = mysqli_connect('localhost','peter','abc123','my_db');
if (!$con)
{
      die('Could not connect: ' . mysqli_error($con));
}
mysqli_select_db($con,"ajax_demo");
$sql="SELECT * FROM user WHERE id = '".$q."'";
$result = mysqli_query($con,$sql);
echo "<table border='1'>
<tr>
<th>Firstname</th>
<th>Lastname</th>
<th>Age</th>
<th>Hometown</th>
<th>Job</th>
</tr>";
while($row = mysqli_fetch_array($result))
{
       echo "<tr>";
       echo "<td>" . $row['FirstName'] . "</td>";
       echo "<td>" . $row['LastName'] . "</td>";
       echo "<td>" . $row['Age'] . "</td>";
       echo "<td>" . $row['Hometown'] . "</td>";
       echo "<td>" . $row['Job'] . "</td>";
       echo "</tr>";
}
echo "</table>";
mysqli_close($con);
?>

Explanation: When a query is sent from JavaScript to a PHP file, what will happen is: