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89 lines
3.2 KiB
Markdown
89 lines
3.2 KiB
Markdown
---
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toc_priority: 37
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toc_title: File
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---
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# File Table Engine {#table_engines-file}
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The File table engine keeps the data in a file in one of the supported [file formats](../../../interfaces/formats.md#formats) (`TabSeparated`, `Native`, etc.).
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Usage scenarios:
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- Data export from ClickHouse to file.
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- Convert data from one format to another.
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- Updating data in ClickHouse via editing a file on a disk.
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## Usage in ClickHouse Server {#usage-in-clickhouse-server}
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``` sql
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File(Format)
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```
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The `Format` parameter specifies one of the available file formats. To perform
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`SELECT` queries, the format must be supported for input, and to perform
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`INSERT` queries – for output. The available formats are listed in the
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[Formats](../../../interfaces/formats.md#formats) section.
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ClickHouse does not allow to specify filesystem path for`File`. It will use folder defined by [path](../../../operations/server-configuration-parameters/settings.md) setting in server configuration.
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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.
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You may manually create this subfolder and file in server filesystem and then [ATTACH](../../../sql-reference/statements/attach.md) it to table information with matching name, so you can query data from that file.
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!!! warning "Warning"
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Be careful with this functionality, 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.
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## Example {#example}
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**1.** Set up the `file_engine_table` table:
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``` sql
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CREATE TABLE file_engine_table (name String, value UInt32) ENGINE=File(TabSeparated)
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```
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By default ClickHouse will create folder `/var/lib/clickhouse/data/default/file_engine_table`.
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**2.** Manually create `/var/lib/clickhouse/data/default/file_engine_table/data.TabSeparated` containing:
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``` bash
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$ cat data.TabSeparated
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one 1
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two 2
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```
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**3.** Query the data:
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``` sql
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SELECT * FROM file_engine_table
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```
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``` text
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┌─name─┬─value─┐
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│ one │ 1 │
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│ two │ 2 │
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└──────┴───────┘
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```
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## Usage in ClickHouse-local {#usage-in-clickhouse-local}
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In [clickhouse-local](../../../operations/utilities/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`. It is possible to read and write compressed files based on an additional engine parameter or file extension (`gz`, `br` or `xz`).
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**Example:**
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``` bash
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$ 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"
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```
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## Details of Implementation {#details-of-implementation}
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- Multiple `SELECT` queries can be performed concurrently, but `INSERT` queries will wait each other.
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- Supported creating new file by `INSERT` query.
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- If file exists, `INSERT` would append new values in it.
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- Not supported:
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- `ALTER`
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- `SELECT ... SAMPLE`
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- Indices
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- Replication
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[Original article](https://clickhouse.tech/docs/en/operations/table_engines/file/) <!--hide-->
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