ClickHouse/docs/zh/operations/table_engines/file.md

<a name="table_engines-file"></a>

# File(InputFormat)

The data source is a file that stores data in one of the supported input formats (TabSeparated, Native, etc.).

Usage examples:

- Data export from ClickHouse to file.
- Convert data from one format to another.
- Updating data in ClickHouse via editing a file on a disk.

## Usage in ClickHouse Server

```
File(Format)
```

`Format` should be supported for either `INSERT` and `SELECT`. For the full list of supported formats see [Formats](../../interfaces/formats.md#formats).

ClickHouse does not allow to specify filesystem path for`File`. It will use folder defined by [path](../server_settings/settings.md) setting in server configuration.

When creating table using `File(Format)` it creates empty subdirectory in that folder. When data is written to that table, it's put into `data.Format` file in that subdirectory.

You may manually create this subfolder and file in server filesystem and then [ATTACH](../../query_language/misc.md) it to table information with matching name, so you can query data from that file.

!!! warning
    Be careful with this funcionality, because ClickHouse does not keep track of external changes to such files. The result of simultaneous writes via ClickHouse and outside of ClickHouse is undefined.

**Example:**

**1.** Set up the `file_engine_table` table:

``` sql
CREATE TABLE file_engine_table (name String, value UInt32) ENGINE=File(TabSeparated)
```

By default ClickHouse will create folder `/var/lib/clickhouse/data/default/file_engine_table`.

**2.** Manually create `/var/lib/clickhouse/data/default/file_engine_table/data.TabSeparated` containing:

```bash
$ cat data.TabSeparated
one	1
two	2
```

**3.** Query the data:

``` sql
SELECT * FROM file_engine_table
```

```
┌─name─┬─value─┐
│ one  │     1 │
│ two  │     2 │
└──────┴───────┘
```

## Usage in Clickhouse-local

In [clickhouse-local](../utils/clickhouse-local.md) File engine accepts file path in addition to `Format`. Default input/output streams can be specified using numeric or human-readable names like `0` or `stdin`, `1` or `stdout`.
**Example:**

```bash
$ echo -e "1,2\n3,4" | clickhouse-local -q "CREATE TABLE table (a Int64, b Int64) ENGINE = File(CSV, stdin); SELECT a, b FROM table; DROP TABLE table"
```

## Details of Implementation

- Reads can be parallel, but not writes
- Not supported:
  - `ALTER`
  - `SELECT ... SAMPLE`
  - Indices
  - Replication

[Original article](https://clickhouse.yandex/docs/en/operations/table_engines/file/) <!--hide-->