Snowflake: Split out CREATE VIEW into its own segment

[wong-codaio]

Brief summary of the change made

Snowflake dialect only: Create a segment specifically for Snowflake's CREATE VIEW statement.

• Removed VIEW from the general CreateStatement in Snowflake.
• Consolidated multiple test files around view creation into a single test file.
• Added test cases to support the existing as well as some additional functionality on CREATE VIEW.

fixes #2000

Context

• There is a CreateStatementSegment in Snowflake that aims to encapsulate all possibilities of CREATE statement in Snowflake. The statement however does not account for the specific needs that is targeted only for CREATE VIEW statement.
• While it is possible to fix Snowflake create view statement results in parse error #2000 by adding extra clauses to the CreateStatement segment, it seems it's more appropriate to create a separate class for CreateViewStatementSegment - Which makes Snowflake more aligns what dialect_ansi does (Ansi also has a dedicated CreateViewStatementSegment.

Are there any other side effects of this change that we should be aware of?

• CREATE VIEW segment type has been changed - from create_statement to create_view_statement in Snowflake dialect.
  • If anyone has written custom rules targeting CREATE VIEW in Snowflake's dialect, and is using create_statement as a check in their matching logic, then it'll no longer work.

Pull Request checklist

• Included test cases to demonstrate any code changes, which may be one or more of the following:
  • .sql/.yml parser test cases in test/fixtures/dialects (note YML files can be auto generated with tox -e generate-fixture-yml).
    • Refactored all CREATE VIEW test cases into a single snowflake_create_view.sql file.
• Added appropriate documentation for the change.
  • Added a link to CREATE VIEW documentation on Snowflake's site.

[wong-codaio]

@tunetheweb @Dikootje - Wanted to get how you guys feel about this change.

• I could fix Snowflake create view statement results in parse error #2000 by adding additional clauses in the CreateStatement segment, but it felt more appropriate to have a dedicated class to handle edge cases around CREATE VIEW, rather than adding more complex logic into the overloaded CreateStatement in Snowflake.

[codecov]

Codecov Report

Merging #2217 (9287986) into main (68f479a) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main     #2217   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          149       149           
  Lines        10825     10829    +4     
=========================================
+ Hits         10825     10829    +4     

Impacted Files	Coverage Δ
src/sqlfluff/dialects/dialect_snowflake.py	100.00% <100.00%> (ø)

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[jpy-git]

• I could fix Snowflake create view statement results in parse error #2000 by adding additional clauses in the CreateStatement segment, but it felt more appropriate to have a dedicated class to handle edge cases around CREATE VIEW, rather than adding more complex logic into the overloaded CreateStatement in Snowflake.

I agree that it's a good to split into it's own segment, it better aligns with the docs and is easier to check/maintain. I imagine all the CREATE statements were originally combined to quickly get the basic statements parsing but as we develop them more we can split them out properly 👍

[jpy-git]

@wong-codaio looks great, thanks! LGTM 🚀 ⭐

[Dikootje]

Thanks guys!