[Feature] add 'create_if_not_exists' for views

[eterna2]

Feature:

Add flag create_if_not_exists for create_view and create_materialized_view.

Background:

Hi, I am using create_view and create_materialized_view to generate views via cli. However, i will like the cli to not throw an error if the views already exists. This PR adds a kwargs create_if_not_exists for create_view and create_materialized_view, which will insert CREATE VIEW {} IF NOT EXISTS if the flag is set.

The default for the flag is False so that everything will be backward compatible.

[eterna2]

@kurtmckee Not sure if you are the right person. Can u help me have a look at this PR?

[kurtmckee]

@eterna2, I don't feel qualified yet to review feature requests; my focus has been ticket triage and bug fixes. The project policy is to have unit tests associated with pull requests, so you'll need to add unit tests that demonstrate that this feature is working.

For example, it will be good to confirm that the function continues to raise an exception when the view already exists (the tests may already check this but you should confirm), and also test that the error is suppressed when create_if_not_exists is True.

@kvesteri, would you review this PR? I'm interested in your thoughts on the parameter name "create_if_not_exists". The implementation seems similar to how "materialized" is supported, but the parameter name seems inaccurate to my eyes and I don't have alternate suggestions.

[eterna2]

Hi, I had changed the kwargs to if_not_exists as requested.

Also made several other changes:

• added kwargs or_replace for CREATE [OR REPLACE|ALTER] [MATERIALIZED] VIEW
• added compilation for mysql, postgres, mssql, and snowflake dialects
• updated flake8 rules specifically for view.py to ignore the long docstr and redefinitions for the dialect specific compilation.

I am actually using this for snowflake specifically.

[eterna2]

Sorry. Some unnecessarily format changes cuz i was using black to quickly do the autoformatting.

[kurtmckee]

Thanks @eterna2! I've kicked off the CI runs. Please also add unit tests that demonstrate the new functionality.

[eterna2]

Hi, I have added the unit tests for the new params. I just wrote the test for the generic use case and postgres.

[eterna2]

Seem like crypto package is raising a deprecation warning. Do u want me to add a marker to the requirement for py3.6?

[kurtmckee]

No, I can add that separately.