planner: Add subquery variables #21943
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Summary of ChangesHello @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, 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. 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.
| - 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. |
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The description states that this variable applies to 'all queries that contain subqueries'. However, the documentation for the SEMI_JOIN_REWRITE hint specifies that it currently only works for EXISTS subqueries. To avoid confusion and ensure technical accuracy, it's better to specify that this variable applies to queries with EXISTS subqueries.1
Also, for better readability, it's better to use 'session or global' instead of 'session/global'.
| - 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 to apply the hint [`SEMI_JOIN_REWRITE`](/optimizer-hints.md#semi_join_rewrite) at the session or global level for all queries that contain `EXISTS` subqueries. |
Style Guide References
Footnotes
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Review aspects: ... Technical accuracy and terminology consistency ↩
| - 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. |
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For better readability, it's better to use "session or global" instead of "session/global". Also, SELECT is a SQL keyword and should be enclosed in backticks for consistency.1
| - 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 to apply the hint [`NO_DECORRELATE`](/optimizer-hints.md#no_decorrelate) at the session or global level for all queries with a subquery in the `SELECT` list. |
Style Guide References
Footnotes
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Code snippets, command names, options, and paths should be in backticks (
`). ↩
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What is the related PR or file link(s)?
pingcap/tidb#63204
pingcap/tidb#63416
Do your changes match any of the following descriptions?