Hi all, I'd like to discuss a challenge regarding the preservation of
column aliases after RelNode optimization in Apache Calcite. Let me outline
the specific problem and potential approaches. Problem Statement:
Currently, when applying RelNode optimization rules, Calcite doesn't
preserve the original output column aliases. While using RelRoot seems like
a potential solution, it introduces complications when the optimal RelNode
is a Sort or similar node. Consider this scenario with a best rel: ` SELECT
column1, ... FROM ... ORDER BY column1 DESC ` If we try to preserve aliases
using RelRoot, it might generate SQL like: ` SELECT column1 AS alias1, ...
FROM ( SELECT ... ORDER BY column1 DESC ) t1 ` This transformation can
break the ORDER BY clause functionality in many compute engines. Questions
for Discussion: 1. Is there an existing mature solution in Calcite for
maintaining output alias consistency after optimization? 2. If not, what
would be the recommended approach when dealing with Sort nodes (or similar
RelNodes) that could be affected by RelRoot-based alias preservation? 3. If
we implement a new solution, should we introduce additional RelOptRules to
optimize the resulting RelNode structure? This would ensure we maintain
both alias consistency and query performance.
I'd appreciate your thoughts and suggestions on this matter, especially
from those who have encountered similar challenges. Best regards, Yanjing
Wang
