## What changes were proposed in this pull request?

This PR updates `sql/README.md` according to the latest console output and removes some unused imports in `sql` module. This is done by manually, so there is no guarantee to remove all unused imports.

## How was this patch tested?

Manual.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11907 from dongjoon-hyun/update_sql_module.