mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-20 05:05:38 +00:00
110 lines
4.0 KiB
Markdown
110 lines
4.0 KiB
Markdown
---
|
||
slug: /en/sql-reference/table-functions/hdfs
|
||
sidebar_position: 80
|
||
sidebar_label: hdfs
|
||
---
|
||
|
||
# hdfs
|
||
|
||
Creates a table from files in HDFS. This table function is similar to [url](../../sql-reference/table-functions/url.md) and [file](../../sql-reference/table-functions/file.md) ones.
|
||
|
||
``` sql
|
||
hdfs(URI, format, structure)
|
||
```
|
||
|
||
**Input parameters**
|
||
|
||
- `URI` — The relative URI to the file in HDFS. Path to file support following globs in readonly mode: `*`, `?`, `{abc,def}` and `{N..M}` where `N`, `M` — numbers, \``'abc', 'def'` — strings.
|
||
- `format` — The [format](../../interfaces/formats.md#formats) of the file.
|
||
- `structure` — Structure of the table. Format `'column1_name column1_type, column2_name column2_type, ...'`.
|
||
|
||
**Returned value**
|
||
|
||
A table with the specified structure for reading or writing data in the specified file.
|
||
|
||
**Example**
|
||
|
||
Table from `hdfs://hdfs1:9000/test` and selection of the first two rows from it:
|
||
|
||
``` 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 │
|
||
└─────────┴─────────┴─────────┘
|
||
```
|
||
|
||
## Globs in path {#globs_in_path}
|
||
|
||
Multiple path components can have globs. For being processed file should exists and matches to the whole path pattern (not only suffix or prefix).
|
||
|
||
- `*` — Substitutes any number of any characters except `/` including empty string.
|
||
- `?` — Substitutes any single character.
|
||
- `{some_string,another_string,yet_another_one}` — Substitutes any of strings `'some_string', 'another_string', 'yet_another_one'`. The strings can contain the `/` symbol.
|
||
- `{N..M}` — Substitutes any number in range from N to M including both borders.
|
||
|
||
Constructions with `{}` are similar to the [remote](../../sql-reference/table-functions/remote.md)) table function.
|
||
|
||
**Example**
|
||
|
||
1. Suppose that we have several files with following URIs on HDFS:
|
||
|
||
- ‘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’
|
||
|
||
2. Query the amount of rows in these files:
|
||
|
||
<!-- -->
|
||
|
||
``` sql
|
||
SELECT count(*)
|
||
FROM hdfs('hdfs://hdfs1:9000/{some,another}_dir/some_file_{1..3}', 'TSV', 'name String, value UInt32')
|
||
```
|
||
|
||
3. Query the amount of rows in all files of these two directories:
|
||
|
||
<!-- -->
|
||
|
||
``` sql
|
||
SELECT count(*)
|
||
FROM hdfs('hdfs://hdfs1:9000/{some,another}_dir/*', 'TSV', 'name String, value UInt32')
|
||
```
|
||
|
||
:::note
|
||
If your listing of files contains number ranges with leading zeros, use the construction with braces for each digit separately or use `?`.
|
||
:::
|
||
|
||
**Example**
|
||
|
||
Query the data from files named `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')
|
||
```
|
||
|
||
## Virtual Columns
|
||
|
||
- `_path` — Path to the file.
|
||
- `_file` — Name of the file.
|
||
|
||
## Storage Settings {#storage-settings}
|
||
|
||
- [hdfs_truncate_on_insert](/docs/en/operations/settings/settings.md#hdfs-truncate-on-insert) - allows to truncate file before insert into it. Disabled by default.
|
||
- [hdfs_create_multiple_files](/docs/en/operations/settings/settings.md#hdfs_allow_create_multiple_files) - allows to create a new file on each insert if format has suffix. Disabled by default.
|
||
- [hdfs_skip_empty_files](/docs/en/operations/settings/settings.md#hdfs_skip_empty_files) - allows to skip empty files while reading. Disabled by default.
|
||
- [ignore_access_denied_multidirectory_globs](/docs/en/operations/settings/settings.md#ignore_access_denied_multidirectory_globs) - allows to ignore permission denied errors for multi-directory globs.
|
||
|
||
**See Also**
|
||
|
||
- [Virtual columns](../../engines/table-engines/index.md#table_engines-virtual_columns)
|