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8.5 KiB
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235 lines
8.5 KiB
Markdown
---
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slug: /en/sql-reference/table-functions/file
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sidebar_position: 60
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sidebar_label: file
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---
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# file
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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.
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The `file` function can be used in `SELECT` and `INSERT` queries to read from or write to files.
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**Syntax**
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``` sql
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file([path_to_archive ::] path [,format] [,structure] [,compression])
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```
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**Parameters**
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- `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).
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- `path_to_archive` - The relative path to a zip/tar/7z archive. Supports the same globs as `path`.
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- `format` — The [format](/docs/en/interfaces/formats.md#formats) of the file.
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- `structure` — Structure of the table. Format: `'column1_name column1_type, column2_name column2_type, ...'`.
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- `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`.
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**Returned value**
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A table for reading or writing data in a file.
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## Examples for Writing to a File
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### Write to a TSV file
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```sql
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INSERT INTO TABLE FUNCTION
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file('test.tsv', 'TSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
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VALUES (1, 2, 3), (3, 2, 1), (1, 3, 2)
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```
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As a result, the data is written into the file `test.tsv`:
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```bash
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# cat /var/lib/clickhouse/user_files/test.tsv
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1 2 3
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3 2 1
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1 3 2
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```
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### Partitioned write to multiple TSV files
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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.
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```sql
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INSERT INTO TABLE FUNCTION
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file('test_{_partition_id}.tsv', 'TSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
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PARTITION BY column3
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VALUES (1, 2, 3), (3, 2, 1), (1, 3, 2)
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```
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As a result, the data is written into three files: `test_1.tsv`, `test_2.tsv`, and `test_3.tsv`.
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```bash
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# cat /var/lib/clickhouse/user_files/test_1.tsv
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3 2 1
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# cat /var/lib/clickhouse/user_files/test_2.tsv
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1 3 2
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# cat /var/lib/clickhouse/user_files/test_3.tsv
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1 2 3
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```
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## Examples for Reading from a File
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### SELECT from a CSV file
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First, set `user_files_path` in the server configuration and prepare a file `test.csv`:
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``` bash
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$ grep user_files_path /etc/clickhouse-server/config.xml
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<user_files_path>/var/lib/clickhouse/user_files/</user_files_path>
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$ cat /var/lib/clickhouse/user_files/test.csv
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1,2,3
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3,2,1
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78,43,45
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```
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Then, read data from `test.csv` into a table and select its first two rows:
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``` sql
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SELECT * FROM
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file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
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LIMIT 2;
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```
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``` text
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┌─column1─┬─column2─┬─column3─┐
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│ 1 │ 2 │ 3 │
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│ 3 │ 2 │ 1 │
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└─────────┴─────────┴─────────┘
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```
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### Inserting data from a file into a table
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``` sql
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INSERT INTO FUNCTION
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file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
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VALUES (1, 2, 3), (3, 2, 1);
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```
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```sql
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SELECT * FROM
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file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32');
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```
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``` text
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┌─column1─┬─column2─┬─column3─┐
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│ 1 │ 2 │ 3 │
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│ 3 │ 2 │ 1 │
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└─────────┴─────────┴─────────┘
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```
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Reading data from `table.csv`, located in `archive1.zip` or/and `archive2.zip`:
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``` sql
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SELECT * FROM file('user_files/archives/archive{1..2}.zip :: table.csv');
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```
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## Globs in path
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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
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directory and does not use globs, a `*` will be implicitly added to the path so
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all the files in the directory are selected.
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- `*` — Represents arbitrarily many characters except `/` but including the empty string.
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- `?` — Represents an arbitrary single character.
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- `{some_string,another_string,yet_another_one}` — Substitutes any of strings `'some_string', 'another_string', 'yet_another_one'`. The strings can contain the `/` symbol.
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- `{N..M}` — Represents any number `>= N` and `<= M`.
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- `**` - Represents all files inside a folder recursively.
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Constructions with `{}` are similar to the [remote](remote.md) and [hdfs](hdfs.md) table functions.
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**Example**
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Suppose there are these files with the following relative paths:
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- `some_dir/some_file_1`
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- `some_dir/some_file_2`
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- `some_dir/some_file_3`
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- `another_dir/some_file_1`
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- `another_dir/some_file_2`
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- `another_dir/some_file_3`
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Query the total number of rows in all files:
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``` sql
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SELECT count(*) FROM file('{some,another}_dir/some_file_{1..3}', 'TSV', 'name String, value UInt32');
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```
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An alternative path expression which achieves the same:
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``` sql
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SELECT count(*) FROM file('{some,another}_dir/*', 'TSV', 'name String, value UInt32');
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```
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Query the total number of rows in `some_dir` using the implicit `*`:
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```sql
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SELECT count(*) FROM file('some_dir', 'TSV', 'name String, value UInt32');
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```
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:::note
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If your listing of files contains number ranges with leading zeros, use the construction with braces for each digit separately or use `?`.
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:::
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**Example**
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Query the total number of rows in files named `file000`, `file001`, ... , `file999`:
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``` sql
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SELECT count(*) FROM file('big_dir/file{0..9}{0..9}{0..9}', 'CSV', 'name String, value UInt32');
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```
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**Example**
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Query the total number of rows from all files inside directory `big_dir/` recursively:
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``` sql
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SELECT count(*) FROM file('big_dir/**', 'CSV', 'name String, value UInt32');
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```
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**Example**
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Query the total number of rows from all files `file002` inside any folder in directory `big_dir/` recursively:
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``` sql
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SELECT count(*) FROM file('big_dir/**/file002', 'CSV', 'name String, value UInt32');
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```
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## Virtual Columns {#virtual-columns}
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- `_path` — Path to the file. Type: `LowCardinalty(String)`.
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- `_file` — Name of the file. Type: `LowCardinalty(String)`.
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- `_size` — Size of the file in bytes. Type: `Nullable(UInt64)`. If the file size is unknown, the value is `NULL`.
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- `_time` — Last modified time of the file. Type: `Nullable(DateTime)`. If the time is unknown, the value is `NULL`.
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## Hive-style partitioning {#hive-style-partitioning}
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When setting `use_hive_partitioning` is set to 1, ClickHouse will detect Hive-style partitioning in the path (`/name=value/`) and will allow to use partition columns as virtual columns in the query. These virtual columns will have the same names as in the partitioned path, but starting with `_`.
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**Example**
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Use virtual column, created with Hive-style partitioning
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``` sql
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SET use_hive_partitioning = 1;
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SELECT * from file('data/path/date=*/country=*/code=*/*.parquet') where _date > '2020-01-01' and _country = 'Netherlands' and _code = 42;
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```
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## Settings {#settings}
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- [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.
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- [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.
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- [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.
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- [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.
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- [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.
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**See Also**
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- [Virtual columns](/docs/en/engines/table-engines/index.md#table_engines-virtual_columns)
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- [Rename files after processing](/docs/en/operations/settings/settings.md#rename_files_after_processing)
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