Answers for "php format date string to yyyy-mm-dd"

php date format dd/mm/yyyy

date("d/m/Y", strtotime($str));

convert dd/mm/yyyy to yyyy-mm-dd in mysql php

$var = '20/04/2012';
$date = str_replace('/', '-', $var);
echo date('Y-m-d', strtotime($date));

php validate date format yyyy-mm-dd

$date="2012-09-12";

if (preg_match("/^[0-9]{4}-(0[1-9]|1[0-2])-(0[1-9]|[1-2][0-9]|3[0-1])$/",$date)) {
    return true;
} else {
    return false;
}