From DATE_FORMAT and back to origin date in mysql date column

[Karl-Arne Gjersøyen]

SELECT DATE_FORMAT(dato, '%e/%c/%Y') AS dato FROM transportdokument WHERE
dato >= '2013-07-20' AND dato <= '2013-07-24' GROUP BY dato DESC is working
perfect in my PHP file.

But I need to transfer the date back from my norwegian formatted date to
the origin date format in WHERE dato >= '$standard_date_format';

What need I do to fix this?

Thanks for your time and help to learn me programming!

Karl