rohangarg opened a new pull request, #12773:
URL: https://github.com/apache/druid/pull/12773
Currently, the first/last string aggregator's `getComparator` method (used
in topN ranking, grouping by ordering, post agg ordering) compares two
aggregator values on `__time` first and then on values. This change makes that
comparator to compare only on values which is the correct behavior. The
numerical first/last aggregators already compare on the values.
The current users who are ordering their results on the string first/last
aggregator would need to augment their queries a `max(timeCol)` aggreagtor to
achieve the same results.
For instance, a query like `SELECT stringCol2, LATEST(stringCol, 1024) as
lat FROM table GROUP BY stringCol2 ORDER BY lat` would need to be rewritten as
`SELECT stringCol2, LATEST(stringCol, 1024) as lat FROM table GROUP BY
stringCol2 ORDER BY MAX(timeCol)`
The ingestion ordering is kept as is it since it doesn't impact the query
results.
This PR has:
- [x] been self-reviewed.
- [ ] using the [concurrency
checklist](https://github.com/apache/druid/blob/master/dev/code-review/concurrency.md)
(Remove this item if the PR doesn't have any relation to concurrency.)
- [ ] added documentation for new or modified features or behaviors.
- [ ] added Javadocs for most classes and all non-trivial methods. Linked
related entities via Javadoc links.
- [ ] added or updated version, license, or notice information in
[licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md)
- [ ] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [x] added unit tests or modified existing tests to cover new code paths,
ensuring the threshold for [code
coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md)
is met.
- [ ] added integration tests.
- [x] been tested in a test Druid cluster.
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