Author: 云峤 <chensong.cs@alibaba-inc.com>
Author: kaka1992 <kaka_1992@163.com>

Closes #5839 from kaka1992/master and squashes the following commits:

b15360d [kaka1992] Fix python unit test in sql/test. =_= I forget to commit this file last time.
f928816 [kaka1992] Fix python style in sql/test.
d2e7f72 [kaka1992] Fix python style in sql/test.
c54d904 [kaka1992] Fix empty map bug.
7e64d1e [云峤] Update
7b9b858 [云峤] undo
f080f8d [云峤] update pep8
76f0c51 [云峤] Merge remote-tracking branch 'remotes/upstream/master'
7d62368 [云峤] [SPARK-7294] ADD BETWEEN
baf839b [云峤] [SPARK-7294] ADD BETWEEN
d11d5b9 [云峤] [SPARK-7294] ADD BETWEEN