Currently, in C++ version of orc. We can only select by filed id or field name. This works fine when data structure is flat such as struct<int1:int, s1:string, list1:array<int>>. But when we have a nested structure, struct<int1:int, struct1:struct<int2:int, long2:long>>. We still can only select the field of int1 and struct1. We can not directly select long2.
We can select long2 by its column id. This can be achieved by updating include function in ReaderOptions.