[GitHub] [calcite] zhztheplayer edited a comment on issue #1087: [CALCITE-1172] Add rule to flatten two Aggregate operators into one

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zhztheplayer edited a comment on issue #1087: [CALCITE-1172] Add rule to flatten two Aggregate operators into one
URL: https://github.com/apache/calcite/pull/1087#issuecomment-480001492
 
 
   Overall I am +1, besides a minor issue (might not be an issue?):
   
   If I test the code correctly, following SQL is still not optimized:
   
   ```sql
   -- 1. bottom count has only an empty group set
   -- 2. query is executed on empty table/set
   select sum(c) from (select count("empid") as c from "hr"."emps" where "deptno" < 0)
   ```
   
   I guess this is because following fail condition is a little aggressive:
   https://github.com/apache/calcite/blob/b5c6e25b131fcfcd5a640641401a8cb61820ad72/core/src/main/java/org/apache/calcite/rel/rules/AggregateMergeRule.java#L121-L123
   
   Could we ensure the optimization happens on such a SQL too? (since it looks like a simplest one)

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