include compatibility notice for tidb_remove_orderby_in_subquery #20684
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Code Review
The pull request includes a compatibility notice for the tidb_remove_orderby_in_subquery system variable. The change involves updating the release notes to reflect a change in the default value of this variable. The pull request description is comprehensive, covering the necessary details and affected versions.
Merge Readiness
The pull request appears to be ready for merging, as it primarily involves documentation updates and includes sufficient information for users to understand the change. I am unable to directly approve the pull request, and users should have others review and approve this code before merging.
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| - The default value of [`tidb_remove_orderby_in_subquery`](/system-variables.md#tidb_remove_orderby_in_subquery-new-in-v610) has been changed from `OFF` to `ON` to avoid unnecessary sorting operations. This change may result in a different order of query results. The ISO/IEC SQL standard does not require query results to follow the ORDER BY sorting of subqueries. To strictly guarantee the final result order, sorting should be explicitly included in the outer query. Applications that rely on subquery sorting can set this variable to `OFF`. Clusters upgraded from older versions will retain the previous behavior by default. |
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| - The default value of [`tidb_remove_orderby_in_subquery`](/system-variables.md#tidb_remove_orderby_in_subquery-new-in-v610) has been changed from `OFF` to `ON` to avoid unnecessary sorting operations. This change may result in a different order of query results. The ISO/IEC SQL standard does not require query results to follow the ORDER BY sorting of subqueries. To strictly guarantee the final result order, sorting should be explicitly included in the outer query. Applications that rely on subquery sorting can set this variable to `OFF`. Clusters upgraded from older versions will retain the previous behavior by default. | |
| - The default value of [`tidb_remove_orderby_in_subquery`](/system-variables.md#tidb_remove_orderby_in_subquery-new-in-v610) has been changed from `OFF` to `ON` to avoid unnecessary sorting operations, which improves query performance in many cases. This change may result in a different order of query results. The ISO/IEC SQL standard does not require query results to follow the ORDER BY sorting of subqueries. To strictly guarantee the final result order, sorting should be explicitly included in the outer query. Applications that rely on subquery sorting can set this variable to `OFF`. Clusters upgraded from older versions will retain the previous behavior by default. |
What is changed, added or deleted? (Required)
Please refer to pingcap/docs-cn#20139
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