[multistage] Fix AVG Return Type

[vvivekiyer]

This PR fixess the return type of AVG aggregation function. The discussion/context behind this change is documented in OSS issue #10318

Added planner tests.

[codecov-commenter]

Codecov Report

Merging #10368 (14fdbe9) into master (c58a01d) will decrease coverage by 1.96%.
The diff coverage is 75.00%.

@@             Coverage Diff              @@
##             master   #10368      +/-   ##
============================================
- Coverage     70.32%   68.37%   -1.96%     
+ Complexity     5940     5937       -3     
============================================
  Files          2035     2033       -2     
  Lines        110228   110193      -35     
  Branches      16748    16751       +3     
============================================
- Hits          77520    75343    -2177     
- Misses        27275    29490    +2215     
+ Partials       5433     5360      -73     

Flag	Coverage Δ
integration1	24.44% <0.00%> (-0.02%)	⬇️
integration2	?
unittests1	67.85% <75.00%> (+0.09%)	⬆️
unittests2	13.76% <0.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...n/java/org/apache/pinot/query/type/TypeSystem.java	75.00% <75.00%> (-25.00%)	⬇️
...pinot/core/data/manager/realtime/TimerService.java	0.00% <0.00%> (-100.00%)	⬇️
...t/core/plan/StreamingInstanceResponsePlanNode.java	0.00% <0.00%> (-100.00%)	⬇️
...ore/operator/streaming/StreamingResponseUtils.java	0.00% <0.00%> (-100.00%)	⬇️
...unting/PerQueryCPUMemAccountantFactoryForTest.java	0.00% <0.00%> (-100.00%)	⬇️
...accounting/CPUMemThreadLevelAccountingObjects.java	0.00% <0.00%> (-93.11%)	⬇️
...he/pinot/common/utils/grpc/GrpcRequestBuilder.java	0.00% <0.00%> (-90.91%)	⬇️
...ator/streaming/StreamingSelectionOnlyOperator.java	0.00% <0.00%> (-90.00%)	⬇️
...he/pinot/core/plan/StreamingSelectionPlanNode.java	0.00% <0.00%> (-88.89%)	⬇️
...lugin/stream/kafka20/KafkaStreamLevelConsumer.java	0.00% <0.00%> (-88.34%)	⬇️
... and 205 more

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[walterddr]

can you also add a test in runtime to make sure avg on a big decimal column returns a big decimal value? (a simple 2 big-decimal that taking an avg resulting in a double-overflowed result should be suffice)

[somandal]

LGTM!

[vvivekiyer]

can you also add a test in runtime to make sure avg on a big decimal column returns a big decimal value? (a simple 2 big-decimal that taking an avg resulting in a double-overflowed result should be suffice)

@walterddr Oh yeah, I tried adding it earlier. There's a existing issue where none of the aggregation functions work on BIG_DECIMAL columns 😅 . I'll spend some time tomorrow debugging and fixing it. We can incorporate the fix in this PR or merge this PR and create a separate one for BIG_DECIMAL aggregate functions. I'm ok either way.

[walterddr]

@walterddr Oh yeah, I tried adding it earlier. There's a existing issue where none of the aggregation functions work on BIG_DECIMAL columns 😅 . I'll spend some time tomorrow debugging and fixing it. We can incorporate the fix in this PR or merge this PR and create a separate one for BIG_DECIMAL aggregate functions. I'm ok either way.

ahh. in this case nvm we can fix in follow up PR