Ajax - MySQL Database
We already know how to run an external PHP script with AJAX, so let's take it
to the next level and pull some data down from a MySQL database. Our "order.html" file and PHP
script will have to be updated and we also need to make a new database.
Create the MySQL Table
To clearly illustrate how easy it is to access information from a database using Ajax, we
are going to build MySQL queries on the fly and display the results on "order.html".
Create a new database or use
an existing one and then import the table ajax_example.sql to that database. This sql file will
create the table ajax_example and insert all the data rows. The table has four columns:
- ae_name - The name of the person
- ae_age - Person's age
- ae_sex - The gender of the person
- ae_wpm - The words per minute that person can type
Update order.html
We want to be able to build queries from our HTML file, so there are a few
form elements that will need to be added. The three inputs we are going to implement are:
- Maximum Age (Text Input) - Let the user select the maximum age to be returned.
- Maximum WPM (Text Input) - Let the user select the maximum wpm to returned.
- Gender (Select Input) - Let the user select the gender of a valid person.
order.html HTML/Javascript Code:
<html>
<body>
<script language="javascript" type="text/javascript">
<!--
//Browser Support Code
function ajaxFunction(){
var ajaxRequest; // The variable that makes Ajax possible!
try{
// Opera 8.0+, Firefox, Safari
ajaxRequest = new XMLHttpRequest();
} catch (e){
// Internet Explorer Browsers
try{
ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try{
ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e){
// Something went wrong
alert("Your browser broke!");
return false;
}
}
}
// Create a function that will receive data sent from the server
ajaxRequest.onreadystatechange = function(){
if(ajaxRequest.readyState == 4){
document.myForm.time.value = ajaxRequest.responseText;
}
}
var age = document.getElementById('age').value;
var wpm = document.getElementById('wpm').value;
var sex = document.getElementById('sex').value;
var queryString = "?age=" + age + "&wpm=" + wpm + "&sex=" + sex;
ajaxRequest.open("GET", "ajax-example.php" + queryString, true);
ajaxRequest.send(null);
}
//-->
</script>
<form name='myForm'>
Max Age: <input type='text' id='age' /> <br />
Max WPM: <input type='text' id='wpm' />
<br />
Sex: <select id='sex'>
<option>m</option>
<option>f</option>
</select>
<input type='button' onclick='ajaxFunction()' value='Query MySQL' />
</form>
</body>
</html>
If the new Javascript code is foreign to you, be sure to check out our lesson on Javascript's getElementById Function.
With our new Javascript code
var queryString = "?age=" + age + "&wpm=" + wpm + "&sex=" + sex;
we have built a query string to pass along the information from our
HTML form to our PHP script.
Ajax - Passing Variables via Query String
A query string is a way of passing information by appending data onto the URL. You may have
often seen it on the web, it's all the information that appears after a question mark "?". When
you submit a form using GET it builds a query string, all we're doing here is manually building our own.
- http://www.tizag.com/somescript.php?variable1=value1&variable2=value2
The left side of the equals operator is the variable name and the right side is the variable's value. Also, each
variable is separated with an ampersand &.
For example, if we wanted to send the variables age, sex, and wpm with values 20, f, 40 to our
PHP script ajax-example.php then
our URL would look like:
- http://www.tizag.com/ajax-example.php?age=20&sex=f&wpm=40
Now we need to build a new PHP script to take these variables and run a MySQL query for us.
Ajax - Create ajax-example.php Script
We already changed the destination URL in our ajaxRequest.open method, now we
need to make a script to grab those variables from the query string and execute a MySQL Query.
We're also going to use a special function mysql_real_escape_string to prevent any
harmful user input from doing something they aren't supposed to (we're going to take steps against SQL Injection).
ajax-example.php Code:
<?php
$dbhost = "localhost";
$dbuser = "dbusername";
$dbpass = "dbpassword";
$dbname = "dbname";
//Connect to MySQL Server
mysql_connect($dbhost, $dbuser, $dbpass);
//Select Database
mysql_select_db($dbname) or die(mysql_error());
// Retrieve data from Query String
$age = $_GET['age'];
$sex = $_GET['sex'];
$wpm = $_GET['wpm'];
// Escape User Input to help prevent SQL Injection
$age = mysql_real_escape_string($age);
$sex = mysql_real_escape_string($sex);
$wpm = mysql_real_escape_string($wpm);
//build query
$query = "SELECT * FROM ajax_example WHERE ae_sex = '$sex'";
if(is_numeric($age))
$query .= " AND ae_age <= $age";
if(is_numeric($wpm))
$query .= " AND ae_wpm <= $wpm";
//Execute query
$qry_result = mysql_query($query) or die(mysql_error());
//Build Result String
$display_string = "<table>";
$display_string .= "<tr>";
$display_string .= "<th>Name</th>";
$display_string .= "<th>Age</th>";
$display_string .= "<th>Sex</th>";
$display_string .= "<th>WPM</th>";
$display_string .= "</tr>";
// Insert a new row in the table for each person returned
while($row = mysql_fetch_array($qry_result)){
$display_string .= "<tr>";
$display_string .= "<td>$row[ae_name]</td>";
$display_string .= "<td>$row[ae_age]</td>";
$display_string .= "<td>$row[ae_sex]</td>";
$display_string .= "<td>$row[ae_wpm]</td>";
$display_string .= "</tr>";
}
echo "Query: " . $query . "<br />";
$display_string .= "</table>";
echo $display_string;
?>
The Next Step - Updating order.html
We have completed our initial order.html and ajax-example.php setup, now
we just need our order.html page to update correctly when a query is returned.
We'll be using a couple advanced Javascript functions to update
a segment of order.html with the MySQL result display_string.
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