/**
* Executes a query that returns 0 or 1 row.
* Throws an exception if the query selects 2 or more rows.
*
* @param string $query The SQL statement.
*
* @return int|string|null The selected row.
*/
public static function executeSingleton0($query)
{
self::logQuery($query);
return self::$dl->executeSingleton0($query);
}