A PHP function to detect and convert dates from different formats into a MySQL-compatible format (YYYY-MM-DD). Full article at: http://imelgrat.me/php/date-formatting-detect-convert/

convert-dates.php

<?php
	/**
	 * @author Ivan Ariel Melgrati
	 * @copyright 2015
	 */


	function convert_date_format($old_date = '')
	{
		$old_date = trim($old_date);

		if (preg_match('/^[0-9]{4}-(0[1-9]|1[0-2])-(0[1-9]|[1-2][0-9]|3[0-1])$/', $old_date)) // MySQL-compatible YYYY-MM-DD format
		{
			$new_date = $old_date;
		}
		elseif (preg_match('/^(0[1-9]|[1-2][0-9]|3[0-1])-(0[1-9]|1[0-2])-[0-9]{4}$/', $old_date)) // DD-MM-YYYY format
		{
			$new_date = substr($old_date, 6, 4) . '-' . substr($old_date, 3, 2) . '-' . substr($old_date, 0, 2);
		}
		elseif (preg_match('/^(0[1-9]|[1-2][0-9]|3[0-1])-(0[1-9]|1[0-2])-[0-9]{2}$/', $old_date)) // DD-MM-YY format
		{
			$new_date = substr($old_date, 6, 4) . '-' . substr($old_date, 3, 2) . '-20' . substr($old_date, 0, 2);
		}
		else // Any other format. Set it as an empty date.
		{
			$new_date = '0000-00-00';
		}
		return $new_date;
	}
?>