mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-15 02:41:59 +00:00
96 lines
3.1 KiB
Markdown
96 lines
3.1 KiB
Markdown
|
|
# hdfs
|
|
|
|
Creates a table from files in HDFS. This table function is similar to [url](url.md) and [file](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](../../query_language/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
|
|
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.
|
|
|
|
**See Also**
|
|
|
|
- [Virtual columns](https://clickhouse.tech/docs/en/operations/table_engines/#table_engines-virtual_columns)
|
|
|
|
[Original article](https://clickhouse.tech/docs/en/query_language/table_functions/hdfs/) <!--hide-->
|