Error in updating a mysql table - php

Question

here I'm trying to display the record of a member and trying to edit the details.
First, I'm fetching the details from a database into textboxes, then, when I should hit the submit button..it should update the entry which is updated and should keep the original value of the textbox which is not updated.
Here's the code :-
The first one is of editmember.php
<?php
session_start();
include 'dbconnector.php';
$receivedusername=$_REQUEST['username'];
$parentusername=$_SESSION['username'];
$_SESSION['cusername']=$receivedusername;
//check session
if((isset($_SESSION['logged'])) && ($_SESSION['logged']==1))
{
//now map the user to it's parent account
$query="select * from master_member where parentusername = '" . $parentusername . "' and currentusername = '" . $receivedusername . "'";
$result=mysql_query($query,$db) or die (mysql_error($db));
if(mysql_num_rows($result) > 0)
{
$row=mysql_fetch_assoc($result);
//account mapped, green signal to proceed
?>
<form action="memberaction.php?action=edit" method="post">
<table>
<tr>
<td>Username : <input type="text" name="usrnm" value="<?php echo ($row['currentusername']); ?>" /></td>
</tr>
<tr>
<td>Email : <input type="text" name="eml" value="<?php echo ($row['currentemail']); ?>" /></td>
</tr>
<tr>
<td><input type="submit" name="submit" value="submit"></td>
</tr>
</table>
</form>
<?php
}
else
{
echo "You aren't authorized to perform this task, redirecting.";
header('refresh:2;URL=members.php');
exit();
}
}
else
{
header('Location:login.php');
exit();
}
?>
memberaction.php
case 'update':
$memberusername=$_SESSION['cusername'];//username of the member, whose account is to be edited.
$parentusername=$_SESSION['username'];//username of the parent.
//since the account is already matched to the parent account before, we do not need to do it again.
//get the field value
$usrnm=(isset($_POST['usrnm'])) ? $_POST['usrnm'] : '';
$eml=(isset($_POST['eml'])) ? $_POST['eml'] : '';
$query="update master_member set currentusername = '" . $usrnm . "' and currentemail = '" . $eml . "' where parentusername = '" . $parentusername . "' and currentusername = '" . $memberusername . "'";
$result=mysql_query($query,$db) or die (mysql_error($db));
if($result)
{
echo "updated";
header('refresh:2;URL=members.php');
exit();
}
else
{
echo "Errors";
}
break;
After I hit the submit button, it displays successfully updated, but no change takes place at the database.
What possible mistake I'm doing ?
My DB structure is like :-
http://sqlfiddle.com/#!2/969c54/2