ClickHouse/docs/zh/engines/table-engines/integrations/hdfs.md
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---
machine_translated: true
machine_translated_rev: 72537a2d527c63c07aa5d2361a8829f3895cf2bd
toc_priority: 36
toc_title: HDFS
---
# HDFS {#table_engines-hdfs}
该引擎提供了集成 [Apache Hadoop](https://en.wikipedia.org/wiki/Apache_Hadoop) 生态系统通过允许管理数据 [HDFS](https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/HdfsDesign.html)通过ClickHouse. 这个引擎是相似的
到 [文件](../special/file.md#table_engines-file) 和 [URL](../special/url.md#table_engines-url) 引擎但提供Hadoop特定的功能。
## 用途 {#usage}
``` sql
ENGINE = HDFS(URI, format)
```
该 `URI` 参数是HDFS中的整个文件URI。
该 `format` 参数指定一种可用的文件格式。 执行
`SELECT` 查询时,格式必须支持输入,并执行
`INSERT` queries for output. The available formats are listed in the
[格式](../../../interfaces/formats.md#formats) 科。
路径部分 `URI` 可能包含水珠。 在这种情况下,表将是只读的。
**示例:**
**1.** 设置 `hdfs_engine_table` 表:
``` sql
CREATE TABLE hdfs_engine_table (name String, value UInt32) ENGINE=HDFS('hdfs://hdfs1:9000/other_storage', 'TSV')
```
**2.** 填充文件:
``` sql
INSERT INTO hdfs_engine_table VALUES ('one', 1), ('two', 2), ('three', 3)
```
**3.** 查询数据:
``` sql
SELECT * FROM hdfs_engine_table LIMIT 2
```
``` text
┌─name─┬─value─┐
│ one │ 1 │
│ two │ 2 │
└──────┴───────┘
```
## 实施细节 {#implementation-details}
- 读取和写入可以并行
- 不支持:
- `ALTER` 和 `SELECT...SAMPLE` 操作。
- 索引。
- 复制。
**路径中的水珠**
多个路径组件可以具有globs。 对于正在处理的文件应该存在并匹配到整个路径模式。 文件列表确定在 `SELECT` (不在 `CREATE` 时刻)。
- `*` — Substitutes any number of any characters except `/` 包括空字符串。
- `?` — Substitutes any single character.
- `{some_string,another_string,yet_another_one}` — Substitutes any of strings `'some_string', 'another_string', 'yet_another_one'`.
- `{N..M}` — Substitutes any number in range from N to M including both borders.
建筑与 `{}` 类似于 [远程](../../../sql-reference/table-functions/remote.md) 表功能。
**示例**
1. 假设我们在HDFS上有几个TSV格式的文件其中包含以下Uri:
- hdfs://hdfs1:9000/some\_dir/some\_file\_1
- hdfs://hdfs1:9000/some\_dir/some\_file\_2
- hdfs://hdfs1:9000/some\_dir/some\_file\_3
- hdfs://hdfs1:9000/another\_dir/some\_file\_1
- hdfs://hdfs1:9000/another\_dir/some\_file\_2
- hdfs://hdfs1:9000/another\_dir/some\_file\_3
1. 有几种方法可以创建由所有六个文件组成的表:
<!-- -->
``` sql
CREATE TABLE table_with_range (name String, value UInt32) ENGINE = HDFS('hdfs://hdfs1:9000/{some,another}_dir/some_file_{1..3}', 'TSV')
```
另一种方式:
``` sql
CREATE TABLE table_with_question_mark (name String, value UInt32) ENGINE = HDFS('hdfs://hdfs1:9000/{some,another}_dir/some_file_?', 'TSV')
```
表由两个目录中的所有文件组成所有文件都应满足query中描述的格式和模式):
``` sql
CREATE TABLE table_with_asterisk (name String, value UInt32) ENGINE = HDFS('hdfs://hdfs1:9000/{some,another}_dir/*', 'TSV')
```
!!! warning "警告"
如果文件列表包含带有前导零的数字范围,请单独使用带有大括号的构造或使用 `?`.
**示例**
创建具有名为文件的表 `file000`, `file001`, … , `file999`:
``` sql
CREARE TABLE big_table (name String, value UInt32) ENGINE = HDFS('hdfs://hdfs1:9000/big_dir/file{0..9}{0..9}{0..9}', 'CSV')
```
## 虚拟列 {#virtual-columns}
- `_path` — Path to the file.
- `_file` — Name of the file.
**另请参阅**
- [虚拟列](../index.md#table_engines-virtual_columns)
[原始文章](https://clickhouse.tech/docs/en/operations/table_engines/hdfs/) <!--hide-->