[GitHub] [druid] himanshug commented on issue #8433: StringDictionaryEncodedColumn dimSelector to return CARDINALITY_UNKNOWN with extractionFn

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himanshug commented on issue #8433: StringDictionaryEncodedColumn dimSelector to return CARDINALITY_UNKNOWN with extractionFn
URL: https://github.com/apache/druid/pull/8433#issuecomment-580698020
 
 
   @gianm IIRC, I hit upon it while working on a VirtualColumn whose makeDimensionSelector did not follow that rule and that led to wrong results for topN query which in that case used `PooledTopNAlgorithm` which expects values to be sorted when cardinality is known .  For explicit extrationFn usage , it is not a problem because TopN uses different algorithm for that specific case which is what I meant by extractionFns being handled specially everywhere.
   
   relaxing the ordering requirement and adding  `DimensionSelector#isDictionarySorted` sounds good to me if/when we need it. I was able to solve my problem some other way, so I just left things on commentary.

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