[GitHub] [doris] nextdreamblue commented on issue #14811: [Bug] agg table and unique table get different result when enable_vectorized_engine=false

[GitBox <gi...@apache.org>]

nextdreamblue commented on issue #14811:
URL: https://github.com/apache/doris/issues/14811#issuecomment-1336727961

   初步分析：
   
   这个地方和行存处理replace聚合的逻辑有关
   
   向量化_agg_key_next_block处理replace是先处理的第一行就是最终行，后续有相同key的值，replace的逻辑是
   if (this->has_set_value()) {
               return;
           }
   有值了就直接丢弃后续的行
   
   非向量化_agg_key_next_row是先获取理论上丢弃的行，然后依次用后续行的值覆盖之前的值，最终处理完所有相同key的行就会得到最终replace的值
   这种情况在处理一个rowset有多个segment，每个segment都有相同key的时候，会把相同key的segment_id小的放到后边处理，导致segment小的行的值会覆盖segment_id大的行，导致repalce的最终结果是返回了一个segment_id小的value
   
   而unique表，把同一个rowset下segment_id小的行置为set_need_skip(true)，后续就直接把这类行淘汰了，最终返回的就是segment_id更大的value
   


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