Merge pull request #633 from yakolee/master

bugfix of mysql parser for #comment
Merge pull request #634 from yakolee/master

improve sqlwall for mysql hints
Merge pull request #635 from yakolee/master

improve sqlwall
Merge pull request #636 from yakolee/master

improve sqlwall
Merge pull request #638 from yakolee/master

improve sqlwall
Merge pull request #640 from yakolee/master

improve sqlwall: update
Revert "improve sqlwall: update"
Merge pull request #641 from zhihang777/revert-640-master

Revert "improve sqlwall: update"
Revert "Revert "improve sqlwall: update""
Merge pull request #642 from alibaba/revert-641-revert-640-master

Revert "Revert "improve sqlwall: update""
Merge pull request #643 from yakolee/master

improve sqlwall