mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-19 14:11:58 +00:00
06aa03f1a7
* Doc fixes: rm anchors <a> * Doc fixes: rm anchors <a> * Doc fixes: fix links * Doc fixes: fix the links
78 lines
2.5 KiB
Markdown
78 lines
2.5 KiB
Markdown
# File(InputFormat) {#table_engines-file}
|
|
|
|
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-->
|