feat(frontend): allow schema change & sink into a CTAS table

[BugenZhao]

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What's changed and what's your intention?

Allow performing schema changes (ALTER TABLE ... [ADD | DROP] COLUMN) on or create a sink into a table created by CREATE TABLE AS statement.

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After #19949, we now have two different methods for retrieving the definition of a table: create_sql and create_sql_purified. Prior to this PR, create_sql always directly return the persisted definition string, while create_sql_purified will re-assemble a definition with all columns qualified based on the TableCatalog.

However, the definitions for CTAS tables are missing, causing create_sql_ast to always return an error. This seems pointless. So this PR makes create_sql_ast also run purification if (and only if) the definition is missing (indicating that it's a CTAS table). This enables replacing functionalities for CTAS table, including schema change and sink-into-table.

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• My PR contains critical fixes that are necessary to be merged into the latest release.

Documentation

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Release note

[BugenZhao]

• feat(frontend): use purified definition for replacing table #20131
• feat(frontend): allow schema change & sink into a CTAS table #20174 👈 (View in Graphite)
• main

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[st1page]

LGTM!