mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-15 02:41:59 +00:00
105 lines
3.2 KiB
Markdown
105 lines
3.2 KiB
Markdown
---
|
||
machine_translated: true
|
||
machine_translated_rev: 72537a2d527c63c07aa5d2361a8829f3895cf2bd
|
||
toc_priority: 45
|
||
toc_title: hdfs
|
||
---
|
||
|
||
# hdfs {#hdfs}
|
||
|
||
从HDFS中的文件创建表。 此表函数类似于 [url](url.md) 和 [文件](file.md) 一些的。
|
||
|
||
``` sql
|
||
hdfs(URI, format, structure)
|
||
```
|
||
|
||
**输入参数**
|
||
|
||
- `URI` — The relative URI to the file in HDFS. Path to file support following globs in readonly mode: `*`, `?`, `{abc,def}` 和 `{N..M}` 哪里 `N`, `M` — numbers, \``'abc', 'def'` — strings.
|
||
- `format` — The [格式](../../interfaces/formats.md#formats) 的文件。
|
||
- `structure` — Structure of the table. Format `'column1_name column1_type, column2_name column2_type, ...'`.
|
||
|
||
**返回值**
|
||
|
||
具有指定结构的表，用于读取或写入指定文件中的数据。
|
||
|
||
**示例**
|
||
|
||
表从 `hdfs://hdfs1:9000/test` 并从中选择前两行:
|
||
|
||
``` sql
|
||
SELECT *
|
||
FROM hdfs('hdfs://hdfs1:9000/test', 'TSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
|
||
LIMIT 2
|
||
```
|
||
|
||
``` text
|
||
┌─column1─┬─column2─┬─column3─┐
|
||
│ 1 │ 2 │ 3 │
|
||
│ 3 │ 2 │ 1 │
|
||
└─────────┴─────────┴─────────┘
|
||
```
|
||
|
||
**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（不仅后缀或前缀）。
|
||
|
||
- `*` — 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 [远程表功能](../../sql-reference/table-functions/remote.md)).
|
||
|
||
**示例**
|
||
|
||
1. 假设我们在HDFS上有几个具有以下Uri的文件:
|
||
|
||
- ‘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. 查询这些文件中的行数:
|
||
|
||
<!-- -->
|
||
|
||
``` sql
|
||
SELECT count(*)
|
||
FROM hdfs('hdfs://hdfs1:9000/{some,another}_dir/some_file_{1..3}', 'TSV', 'name String, value UInt32')
|
||
```
|
||
|
||
1. 查询这两个目录的所有文件中的行数:
|
||
|
||
<!-- -->
|
||
|
||
``` sql
|
||
SELECT count(*)
|
||
FROM hdfs('hdfs://hdfs1:9000/{some,another}_dir/*', 'TSV', 'name String, value UInt32')
|
||
```
|
||
|
||
!!! warning "警告"
|
||
如果您的文件列表包含带前导零的数字范围，请单独使用带大括号的构造或使用 `?`.
|
||
|
||
**示例**
|
||
|
||
从名为 `file000`, `file001`, … , `file999`:
|
||
|
||
``` sql
|
||
SELECT count(*)
|
||
FROM hdfs('hdfs://hdfs1:9000/big_dir/file{0..9}{0..9}{0..9}', 'CSV', 'name String, value UInt32')
|
||
```
|
||
|
||
## 虚拟列 {#virtual-columns}
|
||
|
||
- `_path` — Path to the file.
|
||
- `_file` — Name of the file.
|
||
|
||
**另请参阅**
|
||
|
||
- [虚拟列](https://clickhouse.tech/docs/en/operations/table_engines/#table_engines-virtual_columns)
|
||
|
||
[原始文章](https://clickhouse.tech/docs/en/query_language/table_functions/hdfs/) <!--hide-->
|