[SQL] Minor fix for doc and comment

Author: wangfei <wangfei1@huawei.com>

Closes #3533 from scwf/sql-doc1 and squashes the following commits:

962910b [wangfei] doc and comment fix

(cherry picked from commit 7b79957879db4dfcc7c3601cb40ac4fd576259a5)
Signed-off-by: Michael Armbrust <michael@databricks.com>