Major Description
Original test failure: looks like column type changes to different decimals in most cases. In one case it causes the integer part to be too big to fit, so the result becomes null it seems.
What happens is that CBO adds casts to arithmetic expressions to make them type compatible; these casts become part of new AST, and then Hive adds casts on top of these casts. This (the first part) also causes lots of out file changes. It's not clear how to best fix it so far, in addition to incorrect decimal width and sometimes nulls when width is larger than allowed in Hive.
Option one - don't add those for numeric ops - cannot be done if numeric op is a part of compare, for which CBO needs correct types.
Option two - unwrap casts when determining type in Hive - hard or impossible to tell apart CBO-added casts and user casts.
Option three - don't change types in Hive if CBO has run - seems hacky and hard to ensure it's applied everywhere.
Option four - map all expressions precisely between two trees and remove casts again after optimization, will be pretty difficult.
Option five - somehow mark those casts. Not sure about how yet.