Github user vvysotskyi commented on the issue:
    @paul-rogers, as you know, there were some differences between the commits 
in the older Calcite version (1.4.0-r23) which was used by Drill and commits 
merged into Apache master. One of such commits was `[CALCITE-1150] Add dynamic 
record type and dynamic star for schema-on-read table`. In our older Calcite 
fork `DYNAMIC_STAR` was `*`, but after rebase onto Calcite 1.15, it became `**`.
    As I understand, `DYNAMIC_STAR` itself means "default column" which will be 
added to table row type for the case when we have `select *` query and the 
schema of the underlying table is not known. 
    As for the name of constant, I think current `DYNAMIC_STAR` more suitable, 
since Calcite also uses a similar name for the same string: 
`DynamicRecordType.DYNAMIC_STAR_PREFIX`. So current name at least helps to 
avoid divergence in naming for Drill and Calcite.


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