> For the complete documentation index, see [llms.txt](https://litedb.gitbook.io/litedb-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://litedb.gitbook.io/litedb-docs/sql/dml/update.md).

# UPDATE

UPDATE 语句用于更新集合中已有记录的列值。

执行前需要先 [USE](/litedb-docs/sql/ddl/database/use.md) 切换到目标数据库。

## 语法

```ebnf
update_statement ::=
    UPDATE collection_name
    SET assignment { "," assignment }
    [ WHERE expression ]

collection_name ::= identifier

assignment ::= column_name "=" expression

column_name ::= identifier
```

## 参数

| 参数                  | 说明                                |
| ------------------- | --------------------------------- |
| `collection_name`   | 目标集合名称                            |
| `assignment`        | 赋值项；同一语句中目标列不可重复                  |
| `column_name`       | 要更新的列名称                           |
| `expression`（`SET`） | 新值表达式，可引用同行其他列，例如 `age = age + 1` |
| `WHERE expression`  | 可选过滤条件，结果类型须为 `BOOLEAN`           |

## 说明

* 省略 `WHERE` 时，更新集合中的**全部**记录。
* 赋值表达式的类型须与目标列兼容；将 `NULL` 赋给 `NOT NULL` 列会失败。
* `VARCHAR` 仍受最大长度约束，`VECTOR(n)` 维度须与列定义一致。
* 当前不支持 `LIMIT`、`ORDER BY` 或 `RETURNING`。
* 更新成功后会维护相关标量索引与向量索引。

## 示例

```sql
UPDATE users
SET age = age + 1
WHERE name = 'Ada';

UPDATE users
SET active = false, embedding = [0.2, 0.3, 0.4]
WHERE id = 1;

-- 无 WHERE：更新全部行
UPDATE users
SET active = true;
```


---

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