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Update docs for tidb_allow_function_for_expression_index (pingcap#17794)
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Oreoxmt authored Jun 26, 2024
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50 changes: 38 additions & 12 deletions sql-statements/sql-statement-create-index.md
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Expand Up @@ -171,19 +171,45 @@ CREATE TABLE t1 (
DROP INDEX idx1 ON t1;
```

表达式索引涉及众多表达式。为了确保正确性，当前仅允许经充分测试的一部分函数用于创建表达式索引，即生产环境中仅允许表达式中包含这些函数。这些函数可以通过查询变量 [`tidb_allow_function_for_expression_index`](/system-variables.md#tidb_allow_function_for_expression_index-从-v520-版本开始引入) 得到。在后续版本中，这些函数会持续增加。目前允许的函数如下：

- [`JSON_ARRAY()`](/functions-and-operators/json-functions.md)
- [`JSON_ARRAY_APPEND()`](/functions-and-operators/json-functions.md)
- [`JSON_ARRAY_INSERT()`](/functions-and-operators/json-functions.md)
- [`JSON_CONTAINS()`](/functions-and-operators/json-functions.md)
- [`JSON_CONTAINS_PATH()`](/functions-and-operators/json-functions.md)
- [`JSON_DEPTH()`](/functions-and-operators/json-functions.md)
- [`JSON_EXTRACT()`](/functions-and-operators/json-functions.md)
- [`JSON_INSERT()`](/functions-and-operators/json-functions.md)
- [`JSON_KEYS()`](/functions-and-operators/json-functions.md)
- [`JSON_LENGTH()`](/functions-and-operators/json-functions.md)
- [`JSON_MERGE_PATCH()`](/functions-and-operators/json-functions.md)
- [`JSON_MERGE_PRESERVE()`](/functions-and-operators/json-functions.md)
- [`JSON_OBJECT()`](/functions-and-operators/json-functions.md)
- [`JSON_PRETTY()`](/functions-and-operators/json-functions.md)
- [`JSON_QUOTE()`](/functions-and-operators/json-functions.md)
- [`JSON_REMOVE()`](/functions-and-operators/json-functions.md)
- [`JSON_REPLACE()`](/functions-and-operators/json-functions.md)
- [`JSON_SEARCH()`](/functions-and-operators/json-functions.md)
- [`JSON_SET()`](/functions-and-operators/json-functions.md)
- [`JSON_STORAGE_SIZE()`](/functions-and-operators/json-functions.md)
- [`JSON_TYPE()`](/functions-and-operators/json-functions.md)
- [`JSON_UNQUOTE()`](/functions-and-operators/json-functions.md)
- [`JSON_VALID()`](/functions-and-operators/json-functions.md)
- [`LOWER()`](/functions-and-operators/string-functions.md#lower)
- [`MD5()`](/functions-and-operators/encryption-and-compression-functions.md)
- [`REVERSE()`](/functions-and-operators/string-functions.md#reverse)
- [`TIDB_SHARD()`](/functions-and-operators/tidb-functions.md#tidb_shard)
- [`UPPER()`](/functions-and-operators/string-functions.md#upper)
- [`VITESS_HASH()`](/functions-and-operators/tidb-functions.md)

对于以上列表之外的函数，由于未完成充分测试，当前仍为实验特性，不建议在生产环境中使用。其他的表达式例如运算符、`CAST` 和 `CASE WHEN` 也同样为实验特性，不建议在生产环境中使用。如果仍然希望使用，可以在 [TiDB 配置文件](/tidb-configuration-file.md#allow-expression-index-从-v400-版本开始引入)中进行以下设置：

```sql
allow-expression-index = true
```

> **注意：**
>
> 表达式索引涉及众多表达式。为了确保正确性，当前仅允许经充分测试的一部分函数用于创建表达式索引，即生产环境中仅允许表达式中包含这些函数。这些函数可以通过查询变量 `tidb_allow_function_for_expression_index` 得到。在后续版本中，这些函数会持续增加。目前允许的函数如下:
>
> ```
> JSON_ARRAY, JSON_ARRAY_APPEND, JSON_ARRAY_INSERT, JSON_CONTAINS, JSON_CONTAINS_PATH, JSON_DEPTH, JSON_EXTRACT, JSON_INSERT, JSON_KEYS, JSON_LENGTH, JSON_MERGE_PATCH, JSON_MERGE_PRESERVE, JSON_OBJECT, JSON_PRETTY, JSON_QUOTE, JSON_REMOVE, JSON_REPLACE, JSON_SEARCH, JSON_SET, JSON_STORAGE_SIZE, JSON_TYPE, JSON_UNQUOTE, JSON_VALID, LOWER, MD5, REVERSE, TIDB_SHARD, UPPER, VITESS_HASH
> ```
>
> 对于以上列表之外的函数，由于未完成充分测试，当前仍为实验特性，不建议在生产环境中使用。其他的表达式例如运算符、`CAST` 和 `CASE WHEN` 也同样为实验特性，不建议在生产环境中使用。如果仍然希望使用，可以在 [TiDB 配置文件](/tidb-configuration-file.md#allow-expression-index-从-v400-版本开始引入)中进行以下设置：
>
> ```sql
> allow-expression-index = true
> ```
>
> 表达式索引不能为主键。
>
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4 changes: 2 additions & 2 deletions system-variables.md
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Expand Up @@ -942,8 +942,8 @@ mysql> SHOW GLOBAL VARIABLES LIKE 'max_prepared_stmt_count';
- 作用域：NONE
- 是否受 Hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value) 控制：否
- 默认值：`json_array`、`json_array_append`、`json_array_insert`、`json_contains`、`json_contains_path`、`json_depth`、`json_extract`、`json_insert`、`json_keys`、`json_length`、`json_merge_patch`、`json_merge_preserve`、`json_object`、`json_pretty`、`json_quote`、`json_remove`、`json_replace`、`json_search`、`json_set`、`json_storage_size`、`json_type`、`json_unquote`、`json_valid`、`lower`、`md5`、`reverse`、`tidb_shard`、`upper`、`vitess_hash`
- 这个变量用于显示创建表达式索引所允许使用的函数。
- 默认值：`json_array, json_array_append, json_array_insert, json_contains, json_contains_path, json_depth, json_extract, json_insert, json_keys, json_length, json_merge_patch, json_merge_preserve, json_object, json_pretty, json_quote, json_remove, json_replace, json_search, json_set, json_storage_size, json_type, json_unquote, json_valid, lower, md5, reverse, tidb_shard, upper, vitess_hash`
- 这个只读变量用于显示创建[表达式索引](/sql-statements/sql-statement-create-index.md#表达式索引)所允许使用的函数。
### `tidb_allow_mpp` <span class="version-mark">从 v5.0 版本开始引入</span>
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