[GitHub] [druid] abhishekagarwal87 commented on pull request #13014: Add support for using multiple columns in a distinct count sql aggregation

["abhishekagarwal87 (via GitHub)" <gi...@apache.org>]

abhishekagarwal87 commented on PR #13014:
URL: https://github.com/apache/druid/pull/13014#issuecomment-1523105801

   > Implementation looks OK. I had some comments on the docs.
   > 
   > In thinking about the docs I realized the implementation is limited in various ways:
   > 
   > * Counting distinct tuples approximately apparently requires `druid.sql.approxCountDistinct.function = APPROX_COUNT_DISTINCT_DS_HLL`, so if you have set this to something else then you are out of luck.
   > * Counting distinct tuples approximately cannot be done with `APPROX_COUNT_DISTINCT` or `APPROX_COUNT_DISTINCT_BUILTIN`, since they only support a single argument.
   > 
   > It'd be nice to flesh this out more, so `APPROX_COUNT_DISTINCT_DS_HLL` at least could support distinct tuples, and so people could use the `APPROX_*` functions directly. Perhaps in a follow-up. The only changes I really would like to see in this edition are the doc changes.
   
   Good catch. I think you mean that `druid.sql.approxCountDistinct.function` has to be set to `APPROX_COUNT_DISTINCT_BUILTIN` and not `APPROX_COUNT_DISTINCT_DS_HLL`. can you confirm? 


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