Even though NIST has a conformance test suite for SQL implementations, it is closely tied to U.S. Federal Government requirements and is not always comfortably viewed by users in other nations. All this will be backed up by legal obligations, including a Conformance Statement Questionnaire that every vendor must complete for a product to be branded, identifying all options, limits, and so on that the product provides. It all boils down to the voluntary nature of standards. But that path has proved to be remarkably rocky and ill-defined. And they run a far lower risk of being disappointed.
Nothing stands still, least of all technology.
Undoubtedly, the most dramatic development in SQL since its inception is SQL's addition of object-oriented capabilities to the language. Wherever possible we have identified contact points for further information.