added create and drop schema

[alex-dukhno]

This PR adds functionality to parse CREATE SCHEMA schema_name and DROP SCHEMA schema_name

[nickolay]

Thanks!

Both SQL:2016 and Posgres have a number of options for the CREATE SCHEMA statement. They also support including other CREATE statements as part of the schema definition, rather than separate statements. This PR supports neither (which is fine, but I wanted to mention it).

[nickolay]

I think with the next addition it makes sense to change the message, so that it doesn't duplicate the list above (as it's incorrect already, missing "EXTERNAL").

[alex-dukhno]

Both SQL:2016 and Posgres have a number of options for the CREATE SCHEMA statement. They also support including other CREATE statements as part of the schema definition, rather than separate statements.

I think it will be gradually added. From my side, I am contributing to parser those parts that I need to right now to develop Postgres compatible database 😄 So whenever I need support of including other statements I will come back to this repo 😃

[nickolay]

Yep, I agree that implementing bits and pieces as you need them makes the most sense. Thanks for sharing them!

I'm just making a note of the the relevant docs and the bits that I think are helpful for maintaining and maybe re-using the parser.