A marker interface for all DDL queries.

A lot of DDL queries come with syntax that requires emulation using anonymous blocks via DSL#begin(Statement...). While basic anonymous blocks are supported in the jOOQ Open Source Edition as well, more sophisticated blocks and other procedural logic is a commercial only feature. Examples for this are:

• Various IF [ NOT ] EXISTS clauses.
• ALTER VIEW … AS (emulated via a block containing DROP VIEW and then CREATE VIEW).