You are right, that is fair. Rounding might happen. Overflowing might happen too, though I do not know if there is a deterministic behavior to handle it, e.g., defined by the SQL standard.
When I proposed this fix, I was assuming that this is something that we will document properly on the Hive side, so we can support DECIMAL type (similar to what we do with the handling of NULL semantics by Druid). Are you suggesting that we should not support DECIMAL in Druid?
We could check the precision&scale to control overflow, though user needs to be aware of what is going on in Druid and that rounding might happen.
Ashutosh Chauhan, what do you think? Julian Hyde, could you give your opinion about this too?