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Revert "*: remove expression index out of experimental feature." #4444

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Merged
TomShawn merged 5 commits into from
Dec 18, 2020
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Revert "*: remove expression index out of experimental feature." #4444

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86418d0
Revert "*: remove expression index out of experimental feature."
Joyinqin Dec 18, 2020
14258d7
Update sql-statement-create-index.md
Joyinqin Dec 18, 2020
27723ec
Merge branch 'master' into revert-patch
Joyinqin Dec 18, 2020
4e74496
fix the broken link
Joyinqin Dec 18, 2020
6911286
Merge branch 'revert-patch' of https://github.com/Joyinqin/docs into …
Joyinqin Dec 18, 2020
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12 changes: 12 additions & 0 deletions sql-statements/sql-statement-create-index.md
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Expand Up @@ -111,6 +111,18 @@ Query OK, 0 rows affected (0.31 sec)

## Expression index

> **Note:**
>
> Expression index is still an experimental feature. It is **NOT** recommended that you use it in the production environment.

To use this feature, make the following setting in [TiDB Configuration File](/tidb-configuration-file.md#allow-expression-index-new-in-v400):

{{< copyable "sql" >}}

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

TiDB can build indexes not only on one or more columns in a table, but also on an expression. When queries involve expressions, expression indexes can speed up those queries.

Take the following query as an example:
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7 changes: 6 additions & 1 deletion tidb-configuration-file.md
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Expand Up @@ -612,4 +612,9 @@ For pessimistic transaction usage, refer to [TiDB Pessimistic Transaction Mode](

## experimental

The `experimental` section, introduced in v3.1.0, describes configurations related to the experimental features of TiDB. Currently, this section has no configuration item.
The `experimental` section, introduced in v3.1.0, describes configurations related to the experimental features of TiDB.

### `allow-expression-index` <span class="version-mark">New in v4.0.0</span>

- Determines whether to create the expression index.
- Default value: false