formato de data do php dd / mm / AAAA
date("d/m/Y", strtotime($str));
php converter a data de dd / mm / AAAA para AAAA-mm-dd
$date = DateTime::createFromFormat('d/m/Y', "24/04/2012");
echo $date->format('Y-m-d');
mudar o formato de datetime de Y-m-d H: I: s para d-m-Y em php
$old_date = date('l, F d y h:i:s'); // returns Saturday, January 30 10 02:06:34
$old_date_timestamp = strtotime($old_date);
$new_date = date('Y-m-d H:i:s', $old_date_timestamp);
php mudar o formato da data de d / m / y para y-m-d
$var = '20/04/2012';
$date = str_replace('/', '-', $var);
echo date('Y-m-d', strtotime($date));