Fix timestamp issue in a yaml pipeline that calls SQL transform

[shunping]

Fix an issue when running the following pipeline:

pipeline:
  type: chain
  transforms:
    - type: Create
      name: CreateSampleData
      config:
        elements:
          - { id: 1, name: "John" }
          - { id: 2, name: "Jane" }
    - type: Sql
      name: sql
      config:
        query: >
          SELECT *, CURRENT_TIMESTAMP AS ingest_timestamp FROM PCOLLECTION
    - type: PyTransform
      config:
        constructor: apache_beam.transforms.util.LogElements

Internal bug #434240117

Related issues:

• Fix a logical type issue about JdbcDateType and JdbcTimeType #35243
• Fix post commit xlang jdbcio test failure #35428
• Another attempt to fix timestamp and decimal logical type. #35426
• Fix jdbc logical type issues when running a yaml pipeline. #35659

[gemini-code-assist]

Summary of Changes

Hello @shunping, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an issue related to timestamp handling within YAML pipelines that incorporate SQL transforms. I've updated the schema generation logic to correctly resolve field types, particularly for timestamps, by prioritizing cached schema information. Additionally, I've introduced a new test case to validate the proper functioning of the CURRENT_TIMESTAMP SQL function within these YAML-defined pipelines, ensuring that timestamp values are correctly processed and propagated.

Highlights

• Schema Type Resolution: I've updated the named_fields_to_schema function in sdks/python/apache_beam/typehints/schemas.py to first check for existing type information in a cached schema before inferring types from Python typings. This ensures that previously defined schema types, such as those for timestamps, are correctly preserved.
• SQL Timestamp Test Case: I've added a new test pipeline to sdks/python/apache_beam/yaml/tests/sql.yaml that demonstrates the use of CURRENT_TIMESTAMP within a SQL transform. This test verifies that timestamps generated by SQL are correctly handled within the YAML pipeline.

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[github-actions]

Assigning reviewers:

R: @jrmccluskey for label python.

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[shunping]

Thanks @Abacn for reviewing!

[shunping]

Should we cherry pick this into 2.67? @Abacn @Amar3tto