execute a php file on selection of dropdown value - php

Question

i have been searching a solution for days and i have tried ajax/jquery methods posted online but it just wouldnt work. I have a drop down list which gets its value from the database. On selecting any value apart from "Select", i want to display a value which is called upon by a php file:
here's my code for the form:
<tr>
<fieldset id="Date">
<td class="select"><label><span class="text_9">Date:</span></label></td>
<td><select name="date" id="date">
<option value="">Select</option>
<?php include_once "selectdate.php"?></td>
</select>
</tr>
</fieldset>
</table>
and here's the php to run on selection of the drop down (called retrieve.php)
<?php
include_once "connect.php";
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
$form=$_GET;
$trade=$form['tradetype'];
$metal=$form['metal'];
$amount=$form['amount'];
$date=$form['date'];
$stmt = $conn->query("SELECT Discount FROM Contracts WHERE Trade='$trade' AND Metal='$metal' AND Amount='$amount' AND ExpiryDate='$date'");
while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
echo ($row['Discount']);
}
?>
As you can see, the php to be run uses the value from multiple form elements...
I am very new to jquery/ajax... any help is appreciated as i want the result to be displayed on the same page as the form is. Thank you!

Answer 1

If you want to get data from another file to a select, you should add as option. Plain text inside select will not help you out. So wrap the vales with <option></option>
So change this line,
echo "<option>{$row['Discount']}</option>";
If you want to give values,
echo "<option value='{$row['Discount']}'>{$row['Discount']}</option>";
EDIT
Now onchange of deopdown, date call ajax to do next stuff.
$(document).on("change","#date",function() {
var tradetype = //capture the value here;
var metal = //capture the value here;
var amount = //capture the value here;
$.ajax({
url:"path/filename.php",
data:{date:$(this).val(),"tradetype":tradetype,"metal":metal,"amount":amount},
type: "POST",
success: function(data){
alert(data);//this will alert what you have echoed on php file
}
});
});