Jackie-Jiang commented on PR #19390:
URL: https://github.com/apache/pinot/pull/19390#issuecomment-5458980900
Confirmed and fixed in `2cd84a8`.
`resolveColumnValueIds` delegates its single-value branch to the null-aware
`resolveColumnIds`, but the multi-value branch resolved every element straight
through the on-the-fly dictionary without consulting the null bitmap. Null rows
now take the reserved null component, mirroring the other MV generators:
```java
if (_nullHandlingEnabled) {
RoaringBitmap nullBitmap = blockValSet.getNullBitmap();
if (nullBitmap != null && !nullBitmap.isEmpty()) {
PeekableIntIterator nullIterator = nullBitmap.getIntIterator();
while (nullIterator.hasNext()) {
ids[nullIterator.next()] = _nullComponent;
}
}
}
```
Reusing the existing `_nullComponent` is safe and, I think, the right shape
here: it already stands for a NULL key component when a grouping set excludes a
column, it is already shared across every row and set, and `expandGroupIds`
copies it into a fresh scratch array rather than writing through it. A column
excluded from a set and a column whose value is NULL both render as NULL, which
is why `GROUPING()` exists to tell them apart — so one component serving both
roles matches the semantics. I extended the field's javadoc to say so.
Regression test: `testGroupingSetsOverMultiValueColumnHoldingNulls`, using
your repro shape.
Same note as before on provenance: this one is also pre-existing on master —
its MV resolver has no null-bitmap reference either. My "every group key
generator is null-aware" wording in the description was wrong as written, since
the grouping-sets MV path was outside the change; it is accurate now that this
is fixed.
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