I know there is dimension column, metric column, and timestamp column. For example if I have column A, B, C, and I specify column A and B as dimension, then I think C will not be dimension. My question is what is the column type of C? or can I query column C at all?
If you define column A and B in your ingestion spec but not C, and C appears in some rows, C will be added as a String-typed column for that datasource.
This doc link has more info: http://druid.io/docs/latest/ingestion/schema-design.html