ClickHouse/docs/en/sql-reference/table-functions/hdfs.md

---
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. Type: `LowCardinalty(String)`.
- `_file` — Name of the file. Type: `LowCardinalty(String)`.
- `_size` — Size of the file in bytes. Type: `Nullable(UInt64)`. If the size is unknown, the value is `NULL`.

## 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)