clintropolis opened a new pull request, #13897:
URL: https://github.com/apache/druid/pull/13897
### Description
Do what the title says. The native `nvl` expression, besides being simpler
to evaluate than `case_searched(notnull(...)...)` is vectorized, so this should
result in a performance improvement for any queries that would be otherwise
vectorizable if not for something like a `NVL(x, 'no x')` or `COALESCE(x, 'no
x')`. Multi-argument `COALESCE` still plans to a `CASE` statement, which is not
vectorized.
The built-in `COALESCE` operator definition does some super early mandatory
rewriting into a `CASE` statement a lot earlier than a convertlet could handle
it, so I made custom definitions of `COALESCE` and an `NVL` to match the return
type inference rules to make them consistent since convertlet is rewriting 2
argument `COALESCE` into `NVL`.
#### Release note
SQL operators `NVL` and `COALESCE` with 2 arguments now plan to a native
`nvl` expression, which supports the vector engine. Multi-argument `COALESCE`
still plans into a `case_searched`, which is not vectorized.
<hr>
This PR has:
- [ ] 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.
- [ ] a release note entry in the PR description.
- [ ] 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.
- [ ] 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.
- [ ] been tested in a test Druid cluster.
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