924060929 opened a new pull request, #36128:
URL: https://github.com/apache/doris/pull/36128

   ## Proposed changes
   
   Backend can process distinct aggregate by two method:
   1. use group by key to process distinct, I call it: external distinct of 
aggregate function
   2. use `multi_distinct_xxx` to process distinct, in the corresponding 
aggregate function, I call it: internal distinct of aggregate function
   
   
   This sql should process distinct by the multi distinct function when use 
four phase aggregation:
   The first two phase use group by key: id,  field1 and field2.
   The last two phase use group by key: id. the group by key can not process 
distinct in the aggregate function, so we should use internal distinct method 
in four phase aggregate function, if contains multi distinct column(e.g. field1 
and field2) 
   
   ```sql
   select 
/*+SET_VAR(disable_nereids_rules='TWO_PHASE_AGGREGATE_SINGLE_DISTINCT_TO_MULTI,TWO_PHASE_AGGREGATE_WITH_MULTI_DISTINCT,THREE_PHASE_AGGREGATE_WITH_DISTINCT,THREE_PHASE_AGGREGATE_WITH_COUNT_DISTINCT_MULTI')*/
     id,
     count(distinct field1),
     count(distinct field2)
   from agg_4_phase_tbl2
   group by id
   order by id
   ```
   
   


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