suneet-s commented on a change in pull request #10340:
URL: https://github.com/apache/druid/pull/10340#discussion_r483063690
##########
File path:
extensions-core/stats/src/main/java/org/apache/druid/query/aggregation/variance/VarianceAggregatorFactory.java
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@@ -239,7 +240,9 @@ public Comparator getComparator()
@Override
public Object finalizeComputation(@Nullable Object object)
{
- return object == null ? null : ((VarianceAggregatorCollector)
object).getVariance(isVariancePop);
+ return object == null || ((VarianceAggregatorCollector) object).count == 0
+ ? null
Review comment:
I think so. I was able to hit this bug because of
`VarianceSqlAggregatorTest#testVarianceOrderBy` One of the columns had no value
for a row that was being grouped on.
I then read this comment in `getVariance(...)`
```
// in SQL standard, we should return null for zero elements. But druid there
should not be such a case
```
which is why I returned null.
I guess it could be nicer to return `NullHandling.defaultDoubleValue()`
instead
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