Support of new Syntax

Hello,

a project of the company I am working for, requires a high performance SQL parser such as this one. However, we would mainly require the [Exasol](https://www.exasol.com/) syntax (which is a lot like Oracle syntax) and we may also need DB2 (z/OS and LUW) syntax.

We are considering and willing to implement the needed syntax and would love to officially contribute that syntax here and share it with the community. But before we start working on it, we have to check our internal policies, whether we are allowed to do so or not. Furthermore, we would like to ask you as well for your opinion on this, since Exasol is not a very popular or widespread RDBMS and the readme specifically states the following:
> The most commonly accepted PRs add support for ... a **popular** RDBMS ... will likely be accepted after a brief review.

We want to make sure, that our contribution would be be accepted and supported (being reviewed) by the responsible contributors of this project (of course only if it meets all the standards and contribution guidelines).

I am looking forward to a hopefully positive reply!

该 issue 没有列出文件、测试或入口点。先阅读 README 中关于语法支持和贡献的指导，然后审查当前对各方言的表示方式，再与维护者讨论 Exasol 和 DB2 的范围。Done 要求达成一致的范围和获接受的实现计划，而不只是修改 parser。

由索引模型根据 Issue 内容生成。