mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-30 03:22:14 +00:00
102 lines
3.2 KiB
Markdown
102 lines
3.2 KiB
Markdown
---
|
||
toc_priority: 45
|
||
toc_title: hdfs
|
||
---
|
||
|
||
# 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**
|
||
|
||
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'`.
|
||
- `{N..M}` — Substitutes any number in range from N to M including both borders.
|
||
|
||
Constructions with `{}` are similar to the [remote table function](../../sql-reference/table-functions/remote.md)).
|
||
|
||
**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')
|
||
```
|
||
|
||
!!! warning "Warning"
|
||
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 {#virtual-columns}
|
||
|
||
- `_path` — Path to the file.
|
||
- `_file` — Name of the file.
|
||
|
||
**See Also**
|
||
|
||
- [Virtual columns](../../engines/table-engines/index.md#table_engines-virtual_columns)
|
||
|