LakshSingla opened a new pull request #12017: URL: https://github.com/apache/druid/pull/12017
### Description This is a follow up to the PR #11908. This fixes the bug in top level union all queries when there are more than 2 SQL subqueries are present. For example, if the following query was passed: ``` SELECT channel FROM wikipedia UNION ALL SELECT channel FROM wikipedia WHERE channel = '#en.wikipedia' UNION ALL SELECT channel FROM wikipedia WHERE channel = '#de.wikipedia' ``` it would fail to be explained in the newer format, and would revert to the original plan. Reason for the bug: In the original PR, I assumed that `DruidUnionRel` can only be the top level DruidRel node after parsing, according to the comment [here](https://github.com/apache/druid/blob/1f95a42bb8b32c314934e8e2ecdeb6569c7e8db3/sql/src/main/java/org/apache/druid/sql/calcite/rel/DruidUnionRel.java#L48) When there are more than 2 queries connected by a top level UNION ALL, then the DruidRel structure looks like this: ``` DruidUnionRel DruidRel (query 1) DruidUnionRel DruidRel (query 2) DruidRel (query 3) ``` This PR introduces a recursive method which flattens this structure, and produces the native queries as expected. <hr> ##### Key changed/added classes in this PR * `DruidPlanner` <hr> <!-- Check the items by putting "x" in the brackets for the done things. Not all of these items apply to every PR. Remove the items which are not done or not relevant to the PR. None of the items from the checklist below are strictly necessary, but it would be very helpful if you at least self-review the PR. --> 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. - [x] 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. - [ ] been tested in a test Druid cluster. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
