planner: Add subquery variables #21943

terry1purcell · 2025-10-20T23:42:25Z

First-time contributors' checklist

I've signed the Contributor License Agreement, which is required for the repository owners to accept my contribution.

What is changed, added or deleted? (Required)

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

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

pingcap/tidb#63204
pingcap/tidb#63416

This PR is translated from:
Other reference link(s):

Do your changes match any of the following descriptions?

Delete files
Change aliases
Need modification after applied to another branch
Might cause conflicts after applied to another branch

ti-chi-bot · 2025-10-20T23:42:33Z

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign oreoxmt for approval. For more information see the Code Review Process.
Please ensure that each of them provides their approval before proceeding.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

gemini-code-assist · 2025-10-20T23:42:37Z

Summary of Changes

Hello @terry1purcell, 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 updates the system variables documentation to include two new variables, tidb_opt_enable_no_decorrelate_in_select and tidb_opt_enable_semi_join_rewrite. These additions provide users with clearer information on how to manage optimizer hints for subqueries at both session and global levels, enhancing control over query planning behavior.

Highlights

New System Variable Documentation: Added documentation for the tidb_opt_enable_no_decorrelate_in_select system variable, which controls the application of the NO_DECORRELATE hint for subqueries in the select list.
New System Variable Documentation: Added documentation for the tidb_opt_enable_semi_join_rewrite system variable, which controls the application of the SEMI_JOIN_REWRITE hint for all queries containing subqueries.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	`/gemini review`	Performs a code review for the current pull request in its current state.
Pull Request Summary	`/gemini summary`	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	`/gemini help`	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

gemini-code-assist

Code Review

This pull request adds documentation for two new system variables: tidb_opt_enable_no_decorrelate_in_select and tidb_opt_enable_semi_join_rewrite. The changes are generally good. I've suggested a few minor improvements for clarity and consistency with the style guide. I also pointed out a potential technical inaccuracy in the description of tidb_opt_enable_semi_join_rewrite based on the existing documentation for the corresponding hint.

system-variables.md

Oreoxmt · 2025-10-29T03:45:48Z

@terry1purcell Could you please invite a tech reviewer? Thanks!

Oreoxmt

Rest LGTM

Oreoxmt · 2025-10-30T01:55:02Z

system-variables.md

 - Default value: `OFF`
 - This variable controls whether to enable the [Cross-database binding](/sql-plan-management.md#cross-database-binding) feature.

+### tidb_opt_enable_no_decorrelate_in_select <span class="version-mark">New in v8.5.4</span>


Suggested change

### tidb_opt_enable_no_decorrelate_in_select New in v8.5.4

### tidb_opt_enable_no_decorrelate_in_select New in v8.5.4 and v9.0.0

Oreoxmt · 2025-10-30T01:55:09Z

system-variables.md

+- Default value: `OFF`
+- This variable controls whether to apply the hint [`NO_DECORRELATE`](/optimizer-hints.md#no_decorrelate) at the session/global level for all queries with a subquery in the select list.
+
+### tidb_opt_enable_semi_join_rewrite <span class="version-mark">New in v8.5.4</span>


Suggested change

### tidb_opt_enable_semi_join_rewrite New in v8.5.4

### tidb_opt_enable_semi_join_rewrite New in v8.5.4 and v9.0.0

Oreoxmt · 2025-10-30T01:55:22Z

system-variables.md

+- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
+- Type: Boolean
+- Default value: `OFF`
+- This variable controls whether to apply the hint [`NO_DECORRELATE`](/optimizer-hints.md#no_decorrelate) at the session/global level for all queries with a subquery in the select list.


Suggested change

- This variable controls whether to apply the hint [`NO_DECORRELATE`](/optimizer-hints.md#no_decorrelate) at the session/global level for all queries with a subquery in the select list.

- This variable controls whether the optimizer applies the [`NO_DECORRELATE()`](/optimizer-hints.md#no_decorrelate) hint at the session or global level for all queries that contain a subquery in the `SELECT` list.

Oreoxmt · 2025-10-30T01:55:29Z

system-variables.md

+- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
+- Type: Boolean
+- Default value: `OFF`
+- This variable controls whether to apply the hint [`SEMI_JOIN_REWRITE`](/optimizer-hints.md#semi_join_rewrite) at the session/global level for all queries that contain subqueries.


Suggested change

- This variable controls whether to apply the hint [`SEMI_JOIN_REWRITE`](/optimizer-hints.md#semi_join_rewrite) at the session/global level for all queries that contain subqueries.

- This variable controls whether the optimizer applies the [`SEMI_JOIN_REWRITE()`](/optimizer-hints.md#semi_join_rewrite) hint at the session or global level for all queries that contain subqueries.

ti-chi-bot · 2025-10-30T01:55:48Z

[LGTM Timeline notifier]

Timeline:

2025-10-30 01:55:48.248867473 +0000 UTC m=+1528054.326120053: ☑️ agreed by Oreoxmt.

planner: Add subquery variables

1bbc0a5

ti-chi-bot bot added missing-translation-status This PR does not have translation status info. size/S Denotes a PR that changes 10-29 lines, ignoring generated files. labels Oct 20, 2025

gemini-code-assist bot reviewed Oct 20, 2025

View reviewed changes

system-variables.md Show resolved Hide resolved

system-variables.md Show resolved Hide resolved

Oreoxmt self-assigned this Oct 29, 2025

Oreoxmt added translation/doing This PR's assignee is translating this PR. type/compatibility-or-feature-change This PR involves compatibility changes or feature behavior changes. labels Oct 29, 2025

ti-chi-bot bot removed the missing-translation-status This PR does not have translation status info. label Oct 29, 2025

Oreoxmt self-requested a review October 29, 2025 02:15

Oreoxmt approved these changes Oct 30, 2025

View reviewed changes

ti-chi-bot bot added the needs-1-more-lgtm Indicates a PR needs 1 more LGTM. label Oct 30, 2025

Oreoxmt mentioned this pull request Oct 30, 2025

planner: Add subquery variables pingcap/docs-cn#21032

Open

14 tasks

Oreoxmt added translation/done This PR has been translated from English into Chinese and updated to pingcap/docs-cn in a PR. and removed translation/doing This PR's assignee is translating this PR. labels Oct 30, 2025

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

planner: Add subquery variables #21943

planner: Add subquery variables #21943

terry1purcell commented Oct 20, 2025

Uh oh!

ti-chi-bot bot commented Oct 20, 2025

Uh oh!

gemini-code-assist bot commented Oct 20, 2025

Uh oh!

gemini-code-assist bot left a comment

Uh oh!

Uh oh!

Uh oh!

Oreoxmt commented Oct 29, 2025

Uh oh!

Oreoxmt left a comment

Uh oh!

Oreoxmt Oct 30, 2025

Uh oh!

Oreoxmt Oct 30, 2025

Uh oh!

Oreoxmt Oct 30, 2025

Uh oh!

Oreoxmt Oct 30, 2025

Uh oh!

ti-chi-bot bot commented Oct 30, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

	### tidb_opt_enable_no_decorrelate_in_select <span class="version-mark">New in v8.5.4</span>
	### tidb_opt_enable_no_decorrelate_in_select <span class="version-mark">New in v8.5.4 and v9.0.0</span>

	### tidb_opt_enable_semi_join_rewrite <span class="version-mark">New in v8.5.4</span>
	### tidb_opt_enable_semi_join_rewrite <span class="version-mark">New in v8.5.4 and v9.0.0</span>

	- This variable controls whether to apply the hint [`NO_DECORRELATE`](/optimizer-hints.md#no_decorrelate) at the session/global level for all queries with a subquery in the select list.
	- This variable controls whether the optimizer applies the [`NO_DECORRELATE()`](/optimizer-hints.md#no_decorrelate) hint at the session or global level for all queries that contain a subquery in the `SELECT` list.

planner: Add subquery variables #21943

Are you sure you want to change the base?

planner: Add subquery variables #21943

Conversation

terry1purcell commented Oct 20, 2025

First-time contributors' checklist

What is changed, added or deleted? (Required)

Which TiDB version(s) do your changes apply to? (Required)

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

Do your changes match any of the following descriptions?

Uh oh!

ti-chi-bot bot commented Oct 20, 2025

Uh oh!

gemini-code-assist bot commented Oct 20, 2025

Summary of Changes

Highlights

Footnotes

Uh oh!

gemini-code-assist bot left a comment

Choose a reason for hiding this comment

Code Review

Uh oh!

Uh oh!

Uh oh!

Oreoxmt commented Oct 29, 2025

Uh oh!

Oreoxmt left a comment

Choose a reason for hiding this comment

Uh oh!

Oreoxmt Oct 30, 2025

Choose a reason for hiding this comment

Uh oh!

Oreoxmt Oct 30, 2025

Choose a reason for hiding this comment

Uh oh!

Oreoxmt Oct 30, 2025

Choose a reason for hiding this comment

Uh oh!

Oreoxmt Oct 30, 2025

Choose a reason for hiding this comment

Uh oh!

ti-chi-bot bot commented Oct 30, 2025

[LGTM Timeline notifier]

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants