planner: Add subquery variables (#21943) #22028
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Co-authored-by: Aolin <aolinz@outlook.com>
Co-authored-by: Aolin <aolinz@outlook.com>
Co-authored-by: Aolin <aolinz@outlook.com>
Co-authored-by: Aolin <aolinz@outlook.com>
Co-authored-by: Grace Cai <qqzczy@126.com>
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Summary of ChangesHello @ti-chi-bot, 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 documents two new system variables, Highlights
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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, but I've suggested some improvements to the descriptions for better clarity and technical accuracy, based on the provided style guide.
| - Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No | ||
| - Type: Boolean | ||
| - Default value: `OFF` | ||
| - This variable controls whether the optimizer applies the [`SEMI_JOIN_REWRITE()`](/optimizer-hints.md#semi_join_rewrite) hint for all queries that contain subqueries. |
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The description for this variable seems too general and could be more direct. According to the optimizer-hints.md documentation, the SEMI_JOIN_REWRITE() hint currently only works for EXISTS subqueries. To improve technical accuracy and clarity, I suggest rephrasing the description.12
| - This variable controls whether the optimizer applies the [`SEMI_JOIN_REWRITE()`](/optimizer-hints.md#semi_join_rewrite) hint for all queries that contain subqueries. | |
| - This variable controls whether to rewrite semi-join queries to ordinary join queries for all queries that contain `EXISTS` subqueries. Setting this variable to `ON` has the same effect as adding the [`SEMI_JOIN_REWRITE()`](/optimizer-hints.md#semi_join_rewrite) hint to all applicable queries. |
Style Guide References
Footnotes
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The style guide emphasizes technical accuracy. The current description is too broad and could be misleading, as the underlying hint has a more specific scope. ↩
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The style guide recommends making documentation easy to understand for users. The suggested change explains what the variable does directly, rather than describing it as 'applying a hint', which is more user-friendly. ↩
| - Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes | ||
| - Type: Boolean | ||
| - Default value: `OFF` | ||
| - This variable controls whether the optimizer applies the [`NO_DECORRELATE()`](/optimizer-hints.md#no_decorrelate) hint for all queries that contain a subquery in the `SELECT` list. |
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For better clarity, consider rephrasing the description to explain the variable's effect directly, rather than describing it as 'applying a hint'.1
| - This variable controls whether the optimizer applies the [`NO_DECORRELATE()`](/optimizer-hints.md#no_decorrelate) hint for all queries that contain a subquery in the `SELECT` list. | |
| - This variable controls whether to disable decorrelation for all subqueries in the `SELECT` list. Setting this variable to `ON` has the same effect as adding the [`NO_DECORRELATE()`](/optimizer-hints.md#no_decorrelate) hint to all applicable queries. |
Style Guide References
Footnotes
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The style guide recommends making documentation easy to understand for users. The suggested change explains what the variable does directly, which is more user-friendly. ↩
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This is an automated cherry-pick of #21943
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What is the related PR or file link(s)?
pingcap/tidb#63204
pingcap/tidb#63416
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