lgbo

wait for https://github.com/Kyligence/ClickHouse/pull/175 be merged

The coredump maybe related to one of latest pr in clickhouse backend.

try to rebase to the latest main branch

If don't wrap union exec transformer into a `WholeStageCodegenTransformer `, we need to implement `doExecuteColumnar` for this operator

@zzcclp @rui-mo would you take a review again ? I realize that I may have made something wrong. I should not implement a `TransformSupport` here, but just a columnar alternative...

relate to https://github.com/Kyligence/ClickHouse/pull/160

Compare the two ways to calculate `percent_rank`, get the following flamegraphes ```sql select x, y, percent_rank() over(partition by x order by y) as pr from t1 Format Null settings max_threads=1;...

@nikitamikhaylov I think this PR is ready, could anyone review it ?

> @zzcclp This PR is ready for review.Thanks. In order to support join keys with null correctly, we need change CH's MergeJoinTransform, will add that to CH later. Is there...

will this be merged ?