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

---
slug: /en/sql-reference/table-functions/file
sidebar_position: 60
sidebar_label: file
---

# file

A table engine which provides a table-like interface to SELECT from and INSERT into files, similar to the [s3](/docs/en/sql-reference/table-functions/url.md) table function.  Use `file()` when working with local files, and `s3()` when working with buckets in object storage such as S3, GCS, or MinIO.

The `file` function can be used in `SELECT` and `INSERT` queries to read from or write to files.

**Syntax**

``` sql
file([path_to_archive ::] path [,format] [,structure] [,compression])
```

**Parameters**

- `path` — The relative path to the file from [user_files_path](/docs/en/operations/server-configuration-parameters/settings.md#server_configuration_parameters-user_files_path). Supports in read-only mode the following [globs](#globs-in-path): `*`, `?`, `{abc,def}` (with `'abc'` and `'def'` being strings) and `{N..M}` (with `N` and `M` being numbers).
- `path_to_archive` - The relative path to a zip/tar/7z archive. Supports the same globs as `path`.
- `format` — The [format](/docs/en/interfaces/formats.md#formats) of the file.
- `structure` — Structure of the table. Format: `'column1_name column1_type, column2_name column2_type, ...'`.
- `compression` — The existing compression type when used in a `SELECT` query, or the desired compression type when used in an `INSERT` query. Supported compression types are `gz`, `br`, `xz`, `zst`, `lz4`, and `bz2`.


**Returned value**

A table for reading or writing data in a file.

## Examples for Writing to a File

### Write to a TSV file

```sql
INSERT INTO TABLE FUNCTION
file('test.tsv', 'TSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
VALUES (1, 2, 3), (3, 2, 1), (1, 3, 2)
```

As a result, the data is written into the file `test.tsv`:

```bash
# cat /var/lib/clickhouse/user_files/test.tsv
1	2	3
3	2	1
1	3	2
```

### Partitioned write to multiple TSV files

If you specify a `PARTITION BY` expression when inserting data into a table function of type `file()`, then a separate file is created for each partition. Splitting the data into separate files helps to improve performance of read operations.

```sql
INSERT INTO TABLE FUNCTION
file('test_{_partition_id}.tsv', 'TSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
PARTITION BY column3
VALUES (1, 2, 3), (3, 2, 1), (1, 3, 2)
```

As a result, the data is written into three files: `test_1.tsv`, `test_2.tsv`, and `test_3.tsv`.

```bash
# cat /var/lib/clickhouse/user_files/test_1.tsv
3	2	1

# cat /var/lib/clickhouse/user_files/test_2.tsv
1	3	2

# cat /var/lib/clickhouse/user_files/test_3.tsv
1	2	3
```

## Examples for Reading from a File

### SELECT from a CSV file

First, set `user_files_path` in the server configuration and prepare a file `test.csv`:

``` bash
$ grep user_files_path /etc/clickhouse-server/config.xml
    <user_files_path>/var/lib/clickhouse/user_files/</user_files_path>

$ cat /var/lib/clickhouse/user_files/test.csv
    1,2,3
    3,2,1
    78,43,45
```

Then, read data from `test.csv` into a table and select its first two rows:

``` sql
SELECT * FROM
file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
LIMIT 2;
```

``` text
┌─column1─┬─column2─┬─column3─┐
│       1 │       2 │       3 │
│       3 │       2 │       1 │
└─────────┴─────────┴─────────┘
```

### Inserting data from a file into a table:

``` sql
INSERT INTO FUNCTION
file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
VALUES (1, 2, 3), (3, 2, 1);
```
```sql
SELECT * FROM
file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32');
```

``` text
┌─column1─┬─column2─┬─column3─┐
│       1 │       2 │       3 │
│       3 │       2 │       1 │
└─────────┴─────────┴─────────┘
```

Reading data from `table.csv`, located in `archive1.zip` or/and `archive2.zip`:

``` sql
SELECT * FROM file('user_files/archives/archive{1..2}.zip :: table.csv');
```

## Globs in path 

Paths may use globbing. Files must match the whole path pattern, not only the suffix or prefix. There is one exception that if the path refers to an existing
directory and does not use globs, a `*` will be implicitly added to the path so
all the files in the directory are selected.

- `*` — Represents arbitrarily many characters except `/` but including the empty string.
- `?` — Represents an arbitrary 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}` — Represents any number `>= N` and `<= M`.
- `**` - Represents all files inside a folder recursively.

Constructions with `{}` are similar to the [remote](remote.md) and [hdfs](hdfs.md) table functions.

**Example**

Suppose there are these files with the following relative paths:

- `some_dir/some_file_1`
- `some_dir/some_file_2`
- `some_dir/some_file_3`
- `another_dir/some_file_1`
- `another_dir/some_file_2`
- `another_dir/some_file_3`

Query the total number of rows in all files:

``` sql
SELECT count(*) FROM file('{some,another}_dir/some_file_{1..3}', 'TSV', 'name String, value UInt32');
```

An alternative path expression which achieves the same:

``` sql
SELECT count(*) FROM file('{some,another}_dir/*', 'TSV', 'name String, value UInt32');
```

Query the total number of rows in `some_dir` using the implicit `*`:

```sql
SELECT count(*) FROM file('some_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 total number of rows in files named `file000`, `file001`, ... , `file999`:

``` sql
SELECT count(*) FROM file('big_dir/file{0..9}{0..9}{0..9}', 'CSV', 'name String, value UInt32');
```

**Example**

Query the total number of rows from all files inside directory `big_dir/` recursively:

``` sql
SELECT count(*) FROM file('big_dir/**', 'CSV', 'name String, value UInt32');
```

**Example**

Query the total number of rows from all files `file002` inside any folder in directory `big_dir/` recursively:

``` sql
SELECT count(*) FROM file('big_dir/**/file002', 'CSV', 'name String, value UInt32');
```

## Virtual Columns {#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 file size is unknown, the value is `NULL`.
- `_time` — Last modified time of the file. Type: `Nullable(DateTime)`. If the time is unknown, the value is `NULL`.

## Hive-style partitioning {#hive-style-patitioning}

When setting `use_hive_partitioning` is set to 1, ClickHouse can introduce virtual columns due to Hive partitioning style if the path has the specific structure.

**Example**

Use virtual column, created with Hive-style partitioning

``` sql
SET use_hive_patitioning = 1;
SELECT _specified_column from file('/specified_column=specified_data/file.txt');
```

``` reference
specified_data
```

## Settings {#settings}

- [engine_file_empty_if_not_exists](/docs/en/operations/settings/settings.md#engine-file-empty_if-not-exists) - allows to select empty data from a file that doesn't exist. Disabled by default.
- [engine_file_truncate_on_insert](/docs/en/operations/settings/settings.md#engine-file-truncate-on-insert) - allows to truncate file before insert into it. Disabled by default.
- [engine_file_allow_create_multiple_files](/docs/en/operations/settings/settings.md#engine_file_allow_create_multiple_files) - allows to create a new file on each insert if format has suffix. Disabled by default.
- [engine_file_skip_empty_files](/docs/en/operations/settings/settings.md#engine_file_skip_empty_files) - allows to skip empty files while reading. Disabled by default.
- [storage_file_read_method](/docs/en/operations/settings/settings.md#engine-file-empty_if-not-exists) - method of reading data from storage file, one of: read, pread, mmap (only for clickhouse-local). Default value: `pread` for clickhouse-server, `mmap` for clickhouse-local.


**See Also**

- [Virtual columns](/docs/en/engines/table-engines/index.md#table_engines-virtual_columns)
- [Rename files after processing](/docs/en/operations/settings/settings.md#rename_files_after_processing)