How to validate input field in update profile of a user - php

Question

The Below code is the profile login system update user pade:
In the below code i have already data in the text box(retrive data from database). i want to validate if i erase data and submit:
help me friends i want to validate the input field if the input field is empty:
<?php
session_start(); // Must start session first thing
// Here we run a login check
if (!isset($_SESSION['id'])) {
echo 'Please log in to access your account';
exit();
}
//Connect to the database through our include
include_once "database.php";
// Place Session variable 'id' into local variable
$id = $_SESSION['id'];
// Process the form if it is submitted
if ($_POST['qualific']) {
$fullname = $_POST['fullname'];
$contact = $_POST['contact'];
$qualific = $_POST['qualific'];
$sql = mysql_query("UPDATE jobseeker_members SET fullname='$fullname', contact='$contact', qualification='$qualific' WHERE id='$id'");
echo 'Your account info has been updated, visitors to your profile will now see the new info.<br /><br />
To return to your profile edit area, click here';
exit();
} // close if post
?>
<?php
// Query member data from the database and ready it for display
$sql = mysql_query("SELECT * FROM jobseeker_members WHERE id='$id' LIMIT 1");
while($row = mysql_fetch_array($sql)){
$fullname = $row["fullname"];
$contact = $row["contact"];
$qualific = $row["qualification"];
}
?>
<form action="<?php htmlspecialchars($_SERVER["PHP_SELF"]);?>" method="post" enctype="multipart/form-data" name="form" id="form" onsubmit="return validate_form ( );">
<label>FullName:</label>
<input class="txtbox" name="fullname" type="text" id="fullname"
value="<?php echo "$fullname"?>"/>
<label>Contact No:</label>
<input class="txtbox"name="contact" type="text" id="contact" value="<?php echo "$contact"; ?>" /><br>
<label>Qualification :</label>
<select class="txtbox" name = "qualific">
<option value="<?php echo "$qualific"; ?>"><?php echo "$qualific"; ?></option>
<option value="Below SSC(10 Std)">Below SSC(10 Std)</option>
<option value="SSC(10 Std) passed">SSC(10 Std) passed</option>
<option value="HSC(12 Std) passed">HSC(12 Std) passed</option>
<option value="Graduate">Graduate</option>
<option value="Post Graduate">Post Graduate</option>
</select>
<input class="submitbtn" name="Submit" type="submit" value="Save" />
</form>

Answer 1

just using Multi Conditional IF
if($_POST['fullname'] == '')
{
//value
}
elseif($_POST['qualific'] == '')
{
//value
}
and so on ...
If you want to check the data is changing or not you can use session to hold data from database and campare with data from the form.
while($row = mysql_fetch_array($sql)){
$fullname = $row["fullname"];
// Place Session variable 'fullname'
$fullname = $_SESSION[$fullname];
$contact = $row["contact"];
// Place Session variable 'contact'
$contact = $_SESSION[$contact];
$qualific = $row["qualification"];
// Place Session variable 'qualification'
$qualific = $_SESSION[$qualific];
}
And Compare it :
if($_SESSION['fullname'] !== $_POST['fullname'])
{
// do something
} elseif($_SESSION['fullname'] !== $_POST['fullname']) {
// do something
}
and so on...
btw, sorry for my english