Example Explained - The MySQL Database
The database table we use in the example above looks like this:
| id | FirstName | LastName | Age | Hometown | Job |
|---|---|---|---|---|---|
| 1 | Peter | Griffin | 41 | Quahog | Brewery |
| 2 | Lois | Griffin | 40 | Newport | Piano Teacher |
| 3 | Joseph | Swanson | 39 | Quahog | Police Officer |
| 4 | Glenn | Quagmire | 41 | Quahog | Pilot |
Example Explained
In the example above, when a user selects a person in the dropdown list above, a function called showUser() is executed.
The function is triggered by the onchange event.
Here is the HTML code:
<!DOCTYPE html>
<html>
<head>
<script>
function showUser(str) {
if (str=="") {
document.getElementById("txtHint").innerHTML="";
return;
}
var xmlhttp=new XMLHttpRequest();
xmlhttp.onreadystatechange=function() {
if (this.readyState==4 && this.status==200) {
document.getElementById("txtHint").innerHTML=this.responseText;
}
}
xmlhttp.open("GET","family.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">Joseph Swanson</option>
<option value="4">Glenn Quagmire</option>
</select>
</form>
<br>
<div id="txtHint"><b>Person info will be listed here.</b></div>
</body>
</html>
Code explanation:
First, check if person is selected. If no person is selected (str == ""), clear the content of txtHint and exit the function. If a person is selected, do the following:
- Create an
XMLHttpRequestobject - Create the function to be executed when the server response is ready
- Send the request off to a file on the server
- Notice that a parameter
qis added to the URL (with the content of the dropdown list)
The PHP File
The page on the server called by the JavaScript above is a PHP file called family.php.
The source code in family.php runs a query against a MySQL database, and returns the result in an HTML table:
$q = intval($_GET['q']);
$con = mysqli_connect('localhost','peter','abc123');
if (!$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,$sql);
echo "<table>
<tr>
<th>Firstname</th>
<th>Lastname</th>
<th>Age</th>
<th>Hometown</th>
<th>Job</th>
</tr>";
while($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 the query is sent from the JavaScript to the PHP file, the following happens:
- PHP opens a connection to a MySQL server
- The correct person is found
- An HTML table is created, filled with data, and sent back to the
txtHint placeholder
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