[view] Support CREATE OR REPLACE

[mgorven]

No description provided.

[kurtmckee]

@mgorven Thanks for submitting this!

Would you add some tests that exercise this feature? It looks like these tests will be worthwhile:

• ValueError is raised when materialized and replace are both true
• A view is created when replace is true and it doesn't exist
• A view is replaced when replace is true and it already exists

[mgorven]

Sure. Are there any docs on how to run tests locally? It seems like they require a real database.

[kurtmckee]

That's definitely an area that could be improved. For now, I've kicked off CI for this PR. You should be able to commit additional changes and allow CI to run here.

It appears that CI has started failing, so for the purposes of this PR please disregard the existing failures while working on new tests. Thanks!

[mgorven]

As was discovered in #621, the tests don't actually create views (they create a table). I've changed the tests to run metadata.create_all() instead, which should create the view and backing tables.

[mgorven]

Only test failures are TestAggregatesWithManyToManyRelationships, which are failing in master.

[kurtmckee]

One last thing that I finally realized: the replace parameter needs a bit of documentation in the create_view() docstring.

It'll be rendered automatically the next time the docs are built, and will appear like the other parameters in the create_view() documentation.

[kurtmckee]

Thanks for your work on this, @mgorven!