tidb-cloud: clarify EXCHANGE PARTITION restriction on TiDB X

[AllenMok]

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What is changed, added or deleted? (Required)

The restriction was already documented for tidb_enable_exchange_partition in the System variables section. This PR adds ALTER TABLE ... EXCHANGE PARTITION to Statements > Others and explicitly marks it as not supported on TiDB Cloud Premium, Starter, and Essential.

This makes the corresponding SQL limitation explicit; it does not introduce a new product restriction.

Validation: Markdown lint and git diff --check passed.

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For details, see tips for choosing the affected versions.

• master (the latest development version)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.2 (TiDB 8.2 versions)
• v8.1 (TiDB 8.1 versions)
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• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s): https://docs.pingcap.com/tidbcloud/limited-sql-features-tidb-x/#system-variables

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Summary by CodeRabbit

• Documentation
  • Documented that ALTER TABLE ... EXCHANGE PARTITION is not supported on Premium, Starter, or Essential instances.

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📥 Commits

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• tidb-cloud/limited-sql-features-tidb-x.md

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📝 Walkthrough

Walkthrough

The SQL feature limitations table now documents that ALTER TABLE ... EXCHANGE PARTITION is not supported on Premium, Starter, or Essential instances.

Changes

SQL feature documentation

Layer / File(s)	Summary
Document partition exchange support tidb-cloud/limited-sql-features-tidb-x.md	Adds a table row that marks ALTER TABLE ... EXCHANGE PARTITION as not supported for Premium and Starter/Essential instances.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to 49ecf

This change explicitly documents that EXCHANGE PARTITION is unsupported on TiDB Cloud Premium, Starter, and Essential instances. It is ready to merge with no identified user or production risk.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: documenting the TiDB Cloud restriction for EXCHANGE PARTITION.
Description check	✅ Passed	The description explains the documentation change, affected version, reference link, AI involvement, and validation performed. The required sections are substantially complete.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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