doc: add note about table aliases in FOR UPDATE OF clause

[cryo-zd]

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[gemini-code-assist]

Summary of Changes

Hello, 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 enhances the TiDB documentation for the SELECT statement by incorporating crucial information about the handling of table aliases in the FOR UPDATE OF clause. The update specifically addresses changes introduced in TiDB v8.5.6, providing users with clear guidance on alias usage, ensuring backward compatibility, and explaining how the system resolves potential ambiguities in complex queries involving identically named tables across different databases.

Highlights

• Documentation Update for FOR UPDATE OF Clause: A new note has been added to the SELECT statement documentation, detailing the support for table aliases within the FOR UPDATE OF clause starting from TiDB v8.5.6. This note clarifies behavior regarding backward compatibility, warnings for using base table names when aliases are defined, and how ambiguity is resolved when multiple tables with the same name are involved.

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Changelog

• sql-statements/sql-statement-select.md
  • Added a detailed note explaining the new support for table aliases in the FOR UPDATE OF clause, effective from TiDB v8.5.6.
  • Included guidance on backward compatibility, the issuance of warnings when base table names are used with aliases, and the resolution mechanism for ambiguous table references.

Activity

• The author confirmed completion of the Contributor License Agreement.
• The changes are designated to be applied to the master, v9.0, and v8.5 branches of the documentation.

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Code Review

This pull request adds a helpful note about the new support for table aliases in the FOR UPDATE OF clause. My review includes a suggestion to refine the wording for better clarity and consistency with the documentation style guide, particularly regarding the use of active voice and addressing the user directly.

[gemini-code-assist]

To improve clarity and align with the style guide, I suggest a few wording improvements. This makes the text more direct and easier for users to understand.

Specifically, this suggestion:

• Rewords advising you to use for better conciseness (Style Guide line 24).
• Changes the passive it is recommended to specify to it is recommended that you specify, which is more consistent with the style guide's preference for using the second person ("you") and avoiding passive voice (Style Guide lines 22, 43).

Suggested change

> Starting from v8.5.6, TiDB supports using table aliases in the `FOR UPDATE OF` clause. To maintain backward compatibility, referencing the base table name when an alias is defined is still allowed, but it will trigger a warning advising you to use the explicit alias. When a query involves multiple tables with the same name across different databases (for example, `FROM db1.t, db2.t FOR UPDATE OF t`), TiDB now matches the target table from left to right based on the order in the `FROM` clause, rather than the current database context. To avoid ambiguity, it is recommended to specify the database name or use aliases in the `FOR UPDATE OF` clause.

> Starting from v8.5.6, TiDB supports using table aliases in the `FOR UPDATE OF` clause. To maintain backward compatibility, you can still reference the base table name when an alias is defined, but this triggers a warning that recommends using the explicit alias. When a query involves multiple tables with the same name across different databases (for example, `FROM db1.t, db2.t FOR UPDATE OF t`), TiDB now matches the target table from left to right based on the order in the `FROM` clause, rather than the current database context. To avoid ambiguity, it is recommended that you specify the database name or use aliases in the `FOR UPDATE OF` clause.

References

1. The documentation should be written in the second person ('you') when addressing users. ^(link)
2. The documentation should avoid unnecessary words and repetition for conciseness. ^(link)
3. The documentation should avoid overuse of passive voice. ^(link)