ClickHouse/docs/zh/sql-reference/table-functions/hdfs.md
Ivan Blinkov cd14f9ebcb
SQL reference refactoring (#10857)
* split up select.md

* array-join.md basic refactoring

* distinct.md basic refactoring

* format.md basic refactoring

* from.md basic refactoring

* group-by.md basic refactoring

* having.md basic refactoring

* additional index.md refactoring

* into-outfile.md basic refactoring

* join.md basic refactoring

* limit.md basic refactoring

* limit-by.md basic refactoring

* order-by.md basic refactoring

* prewhere.md basic refactoring

* adjust operators/index.md links

* adjust sample.md links

* adjust more links

* adjust operatots links

* fix some links

* adjust aggregate function article titles

* basic refactor of remaining select clauses

* absolute paths in make_links.sh

* run make_links.sh

* remove old select.md locations

* translate docs/es

* translate docs/fr

* translate docs/fa

* remove old operators.md location

* change operators.md links

* adjust links in docs/es

* adjust links in docs/es

* minor texts adjustments

* wip

* update machine translations to use new links

* fix changelog

* es build fixes

* get rid of some select.md links

* temporary adjust ru links

* temporary adjust more ru links

* improve curly brace handling

* adjust ru as well

* fa build fix

* ru link fixes

* zh link fixes

* temporary disable part of anchor checks
2020-05-15 07:34:54 +03:00

3.2 KiB
Raw Blame History

machine_translated machine_translated_rev toc_priority toc_title
true 72537a2d52 45 hdfs

hdfs

从HDFS中的文件创建表。 此表函数类似于 url文件 一些的。

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}{N..M} 哪里 N, M — numbers, `'abc', 'def' — strings.
  • format — The 格式 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:

SELECT *
FROM hdfs('hdfs://hdfs1:9000/test', 'TSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
LIMIT 2
┌─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).

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:
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:
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:

SELECT count(*)
FROM hdfs('hdfs://hdfs1:9000/big_dir/file{0..9}{0..9}{0..9}', 'CSV', 'name String, value UInt32')

虚拟列

  • _path — Path to the file.
  • _file — Name of the file.

另请参阅

原始文章