> 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/ddl/collection/describe.md).

# DESCRIBE

DESCRIBE 语句用于查看集合的结构。`DESC` 是 `DESCRIBE` 的简写。

查看集合前需要先 [USE](/litedb-docs/sql/ddl/database/use.md) 到目标数据库。

## 语法

```ebnf
describe_statement ::= (DESCRIBE | DESC) [ COLLECTION ] collection_name

collection_name ::= identifier
```

## 参数

| 参数                | 说明          |
| ----------------- | ----------- |
| `COLLECTION`      | 可选关键字，不影响语义 |
| `collection_name` | 集合名称        |

## 返回结果

每一列对应结果集中的一行：

| 列名                   | 类型        | 说明                                       |
| -------------------- | --------- | ---------------------------------------- |
| `column_name`        | `VARCHAR` | 列名称                                      |
| `type`               | `VARCHAR` | 列类型，如 `BIGINT`、`VARCHAR(64)`、`VECTOR(3)` |
| `nullable`           | `BOOLEAN` | 是否可空                                     |
| `unique`             | `BOOLEAN` | 是否声明了 `UNIQUE`                           |
| `comment`            | `VARCHAR` | 列注释；无则为 `NULL`                           |
| `collection_comment` | `VARCHAR` | 集合注释；无则为 `NULL`（各行重复同一值）                 |

## 示例

```sql
DESCRIBE users;
DESC users;
DESCRIBE COLLECTION users;
```


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