### What changes were proposed in this pull request?
This PR is a follow-up of #31061. It fixes a typo in a document: `Finctions` -> `Functions`
### Why are the changes needed?
Make the change better documented.
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
N/A
Closes#31069 from kiszk/SPARK-34022-followup.
Authored-by: Kazuaki Ishizaki <ishizaki@jp.ibm.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>
### What changes were proposed in this pull request?
This PR adds the support of the latest mkdocs, and makes the sidebar properly show. It works in lower versions too.
Before:
After:
### Why are the changes needed?
This is a regression in the documentation.
### Does this PR introduce _any_ user-facing change?
Technically no. It's not related yet. It fixes the list on the sidebar appears properly.
### How was this patch tested?
Manually built the docs via `./sql/create-docs.sh` and `open ./sql/site/index.html`
Closes#31061 from HyukjinKwon/SPARK-34022.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
### What changes were proposed in this pull request?
\_FUNC\_ is used in note() of `ExpressionDescription` since https://github.com/apache/spark/pull/28248, it can be more cases later, we should replace it with function name for documentation
### Why are the changes needed?
doc fix
### Does this PR introduce any user-facing change?
no
### How was this patch tested?
pass Jenkins, and verify locally with Jekyll serve
Closes#28305 from yaooqinn/SPARK-31474-F.
Authored-by: Kent Yao <yaooqinn@hotmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
