public void setIsGenerated(boolean isGenerated) {
    this.isGenerated = isGenerated;
  }
Is this column a generated column, i.e., a column
that is generated from table schema when Hive inserting SEL op for column pruning.
This column has no relation with the input query.

This is used for nested column pruning where we could have the following scenario:
  ...
   |
  SEL (use a)
   |
  OP (use a.f)
   |
  ...
Without this field we do not know whether the column 'a' is actually specified in
the input query or an inserted op by Hive. For the former case, the pruning needs
to produce 'a', while for the latter case, it should produce 'a.f'.
ql/src/java/org/apache/hadoop/hive/ql/plan/ExprNodeColumnDesc.java