[GitHub] [incubator-shardingsphere] terrymanu opened a new issue #3627: Refactor DISTINCT SQL merge

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terrymanu opened a new issue #3627: Refactor DISTINCT SQL merge
URL: https://github.com/apache/incubator-shardingsphere/issues/3627
 
 
   Current distinct process logic is too complicated and mix the logic with execute module and merge module.
   We need to refactor it.
   
   - [ ] Reuse GROUP BY's logic to process DISTINCT row, add all DISTINCT projections in to group by items
   - [ ] Refactor `SUM (DISTINCT xxx)` and `COUNT (DISTINCT xxx)` from QueryResult to `GroupByStreamMergedResult` and `GroupByMemoryMergedResult`
   - [ ] Add `DistinctSumAggregationUnit`, `DistinctCountAggregationUnit` and `DistinctAverageAggregationUnit` to handle aggregation with distinct
   - [ ] Do not need care about `MAX (DISTINCT xxx)` and `MIN (DISTINCT xxx)`, just use regular GROUP BY logic
   - [ ] Remove all distinct logic from execute module

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