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Nov 7, 2025
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planner: Add subquery variables #21943

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planner: Add subquery variables
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18 changes: 18 additions & 0 deletions system-variables.md
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Expand Up @@ -4104,6 +4104,24 @@ mysql> desc select count(distinct a) from test.t;
- 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 and v9.0.0</span>

- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- 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.

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

- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- 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.

### tidb_opt_fix_control <span class="version-mark">New in v6.5.3 and v7.1.0</span>

<CustomContent platform="tidb">
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