/** append a SQL string to the query field. Return the added SQL.
	* @param columnNames Array with columnNames. If the names need to be prefixed, they must already be prefixed.
	* @param tableName String May also hold a String with a Join of tablenames
	*/
	function select_from($columnNames, $tableName, $distinct=false) {	
		$sql  = 'SELECT ';
		if ($distinct) $sql .= 'DISTINCT ';
		$sql .= implode(', ', $columnNames);
		$sql .= " FROM $tableName";
		
		$this->query .= $sql;
		
		return $sql;
	}