I'd have to agreee with PFM. Your best bet would be to use a script to add the dates to a new column called bday or something like that, keeping the original birthday column as you have it already, and putting proper date formats in those date fields. For example use the following script. It will add the field `bday` to your table `employees` and update each of the birthdays
<?php
/**
* @author Jay Gilford
*/
mysql_connect('localhost','root',''); //Change these to your database login details
mysql_select_db('test'); //Change this to your database name
$query = "ALTER TABLE `employees` ADD `bday` date";
mysql_query($query);
$query = "SELECT `id`, `birthday` FROM `employees`";
$res = mysql_query($query);
while($row = mysql_fetch_assoc($res)) {
$query = sprintf("UPDATE `employees` SET `bday` = '%s' WHERE `id` = '%s'",
date('Y-m-d', $row['birthday']),
$row['id']);
mysql_query($query);
}