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!

Der Issue nennt keine Dateien, Tests oder Einstiegspunkte. Beginne damit, die Syntax-Unterstützung und die Hinweise für Beiträge in der README zu lesen, und prüfe anschließend, wie Dialekte derzeit dargestellt werden, bevor du den Umfang für Exasol und DB2 mit den Maintainer:innen besprichst. Done erfordert einen abgestimmten Umfang und einen akzeptierten Implementierungsplan, nicht nur eine Parser-Änderung.

Vom Indexierungsmodell aus dem Issue-Text verfasst.