{"_yql_row_spec"={
        "Type"=["StructType";[
                ["key";["DataType";"Uint32"]];
                ["subkey";["DataType";"Uint32"]];
                ["value";["OptionalType";["TupleType";[["DataType";"Int32"];["OptionalType"; ["OptionalType";["DataType";"Double"]]]]]]
                ];
        ]];
}}