CTAS partition parquet file with non existant columns

Drill allows to create parquet files with partition and metadata that allow potential pruning.

Currently the "PARTITION BY" can only apply on present-column.

It will be useful to have the possibility to allow PARTITION BY on "non-present data" or "computed data"

Examples :

• I have a,b and c, and I want to put only "b" and "c" in the parquet but partition on "a"
• I have a,b and c, and I want to put "a", "b" and "c" in the parquet and partition NOT on a but on myfct(a)