1 PASSTHRU ( Expression 2? 2.0? TO DatabaseReference 2.1? VALUES ( )DELIM 2.1.1+ , 2.1.1 Expression 2.1.2 ) 2 (1) , 2.1+ , 2.1 Expression 2.1.1 ) WHERE 1 DatabaseReference = Database . DataSourceClause 1 DataSourceClause = 2 DataSourceName 2 { DataSourceExpression }