MySQL: Get formatted ISO date from string with european date (can be easily extended to other formats)

getSqlDate.sql

/**
 * This script has been tested in MySQL 5.1.37.
 * It might work with other SQL-DBMS as well.
 */
DROP FUNCTION IF EXISTS getSqlDate;
DELIMITER //

CREATE FUNCTION getSqlDate(str VARCHAR(10))
RETURNS VARCHAR(10) DETERMINISTIC
CASE
    WHEN (str REGEXP '^[0-3][0-9]\.[01][0-9]\.[0-9]{4}$') THEN
        /* European: 01.06.2011 */
        RETURN STR_TO_DATE(str, GET_FORMAT(DATE, 'EUR'));
    WHEN (str REGEXP '^[0-9]{4}-[01][0-9]-[0-3][0-9]$') THEN
        /* ISO 8601: 2011-06-01 */
        RETURN str;
    ELSE
        RETURN 'ERR';
END CASE;
//

DELIMITER ;

SELECT 
    @eur := '01.01.2011' eur_date,
    @iso := '2011-01-01' iso_date,
    STR_TO_DATE(@eur, GET_FORMAT(DATE, 'EUR')) eur_str2date,
    STR_TO_DATE(@iso, GET_FORMAT(DATE, 'ISO')) iso_str2date,
    (@eur REGEXP '^[0-3][0-9]\.[01][0-9]\.20[0-9]{2}$') eur_valid_date,
    (@iso REGEXP '^20[0-9]{2}-[01][0-9]-[0-3][0-9]$') iso_valid_date,
    @date := @eur test_date,
    getSqlDate(@date) test_date_out;

/**
 * Output:
 * +------------+------------+--------------+--------------+----------------+----------------+------------+---------------+
 * | eur_date   | iso_date   | eur_str2date | iso_str2date | eur_valid_date | iso_valid_date | test_date  | test_date_out |
 * +------------+------------+--------------+--------------+----------------+----------------+------------+---------------+
 * | 01.01.2011 | 2011-01-01 | 2011-01-01   | 2011-01-01   |              1 |              1 | 01.01.2011 | 2011-01-01    | 
 * +------------+------------+--------------+--------------+----------------+----------------+------------+---------------+
 */

The multitude of date formats really is a big mess. You never know in what order the parts come, although sometimes you can guess.

I prefer the ISO format. Not only is it the standard here in Sweden, but it's also makes dates sortable as strings.

By the way... Is your code written for some particular database server/engine (e.g. MySQL)?

I agree with you. The code is written and tested in MySQL - thanks for asking. I've just added the info to the gist.