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sysvar: add tidb_enable_strict_not_null_check #22859

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sysvar: add tidb_enable_strict_not_null_check #22859

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Auto-sync: Update English docs from Chinese PR
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1 change: 1 addition & 0 deletions resources/terms.md
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Expand Up @@ -16,6 +16,7 @@
| algorithm | 算法 | |
| anonymous | 匿名 | |
| appendix | 附录 | |
| Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): | 是否受 Hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value) 控制： | |

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{"message": "[PingCAP.ZhPunctuation] Don't use Chinese punctuation (：) in English text.", "location": {"path": "resources/terms.md", "range": {"start": {"line": 19, "column": 145}}}, "severity": "ERROR"}
| architecture | 架构 | |
| arithmetic operation | 数值运算/算术运算 | |
| ascending order | 正序 | |
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20 changes: 20 additions & 0 deletions system-variables.md
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Expand Up @@ -2857,6 +2857,26 @@ Assume that you have a cluster with 4 TiDB nodes and multiple TiKV nodes. In thi
- Default value: `ON`
- This variable is used to control whether to enable the statement summary feature. If enabled, SQL execution information like time consumption is recorded to the `information_schema.STATEMENTS_SUMMARY` system table to identify and troubleshoot SQL performance issues.

### `tidb_enable_strict_not_null_check` <span class="version-mark">New in 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: `ON`
- This variable controls whether TiDB performs strict validation when an `INSERT` statement explicitly writes a `NULL` value to a `NOT NULL` column.
- Possible values:
- `ON`: Enables strict `NOT NULL` validation. This behavior is closer to MySQL 8.0 semantics.
- In strict SQL mode, if you insert a `NULL` value into a `NOT NULL` column, TiDB returns an error.
- In non-strict SQL mode: for a single-row `INSERT` statement, if you insert a `NULL` value into a `NOT NULL` column, TiDB returns an error; for a multi-row `INSERT` statement, if you insert a `NULL` value into a `NOT NULL` column, TiDB downgrades the error to a warning and writes the implicit default value of the column data type.
- `OFF`: Disables strict `NOT NULL` validation for compatibility with the permissive behavior in earlier TiDB versions. When disabled, if you insert a `NULL` value into a `NOT NULL` column, TiDB downgrades the error to a warning and writes the implicit default value for the column data type. For example, TiDB writes `0` for numeric types and an empty string `''` for string types.

> **Note:**
>
> - Earlier TiDB versions were permissive in validating `NOT NULL` constraints. When you insert a `NULL` value into a `NOT NULL` column, TiDB automatically writes the implicit default value of the column data type. Starting from v8.5.0, TiDB tightened this validation: even in non-strict SQL mode, inserting a `NULL` value into a `NOT NULL` column might return an error. This behavior is closer to MySQL 8.0 semantics but might affect applications that depend on the earlier permissive behavior.
>
> - If you upgrade from an earlier TiDB version to a version where strict `NOT NULL` validation is enabled, and your existing application logic depends on the behavior of automatically using implicit default values after writing `NULL` to `NOT NULL` columns, related SQL statements might return errors after the upgrade. If you cannot immediately modify the business logic, you can temporarily set this variable to `OFF` to reduce upgrade compatibility risks. It is recommended that you later update the application logic to avoid explicitly writing `NULL` values to `NOT NULL` columns.

### tidb_enable_strict_double_type_check <span class="version-mark">New in v5.0</span>

- Scope: SESSION | GLOBAL
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