## What changes were proposed in this pull request?
 Add  SQL function - RIGHT && LEFT, same as MySQL:
https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_left
https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_right

## How was this patch tested?
unit test

Author: liuxian <liu.xian3@zte.com.cn>

Closes #18228 from 10110346/lx-wip-0607.