foxtail463 opened a new pull request, #64032:
URL: https://github.com/apache/doris/pull/64032

   Problem Summary:
   
   Scan partition pruning state was not consistently represented across OLAP 
and external file scans. As a result, CBO row-count estimation needed scattered 
special handling and could not reliably use the selected partitions produced by 
pruning.
   
   In addition, partition predicates that had already been applied during 
partition pruning could still be applied again by filter estimation, causing 
duplicated selectivity estimation. HMS selected-partition row-count estimation 
also had unclear handling for valid zero-row results versus unknown row count.
   
   Solution:
   
   Introduce a unified partition selection state carried by scan plans, 
including selected partitions, prune status, manual partition constraints, and 
partition conjuncts already applied to row-count estimation.
   
   Use selected partitions to estimate scan row count for both OLAP and 
external file scans. Preserve applied partition conjuncts in Statistics so 
FilterEstimation can skip predicates that have already affected row count. Also 
clarify HMS selected-partition row-count handling so zero-row results are 
treated as valid instead of unknown.


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