I'm coding to search data by compare datetime. In web form, user input value '2012-06-04' store in $_REQUEST['dateSearch']. I create datetime object from that:

$dateObj = date_create_from_format("Y-m-d",$_REQUEST['dateSearch']);
$dateParam = $dateObj->format("Y-m");

Then I use $dateParam in sql query to find data

$sql = "
    SELECT *
    FROM `temp` as `t`
    WHERE `t`.`date` LIKE '$dateParam%'
";

Everything is ok, but I'm not sure mySQL alway use only one datetime format "Y-m-d H:i:s". At here, $dateParam = $dateObj->format("Y-m"); I set default format is "Y-m". Is the default format never change? I don't want hard set format "Y-m-d H:i:s" in code, instead of, I think get format string from system to use is better. How do I get default datetime format string from mySQL???