Update Hook gets not triggered

Hi,
i try to develop a module, and it works fine except from the update function in the install file. When i start the update process my module is not even in the list of modules.

My update method looks like this:

function basisFunctions_update_6001() {
$ret = array();
$ret[] = update_sql("CREATE TABLE IF NOT EXISTS ... ");
return $ret;
}

Thanks for your help.
Regards francula