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6.0 KiB
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202 lines
6.0 KiB
Markdown
---
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slug: /en/sql-reference/table-functions/file
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sidebar_position: 37
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sidebar_label: file
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---
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# file
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Provides a table-like interface to SELECT from and INSERT to files. This table function is 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 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 [,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). Path to file support following globs in read-only mode: `*`, `?`, `{abc,def}` and `{N..M}` where `N`, `M` — numbers, `'abc', 'def'` — strings.
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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. The supported compression types are `gz`, `br`, `xz`, `zst`, `lz4`, and `bz2`.
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**Returned value**
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A table with the specified structure for reading or writing data in the specified file.
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## File Write Examples
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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 `PARTITION BY` expression when inserting data into a file() function, a separate file is created for each partition value. Splitting the data into separate files helps to improve reading operations efficiency.
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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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## File Read Examples
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### SELECT from a CSV file
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Setting `user_files_path` and the contents of the 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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Getting data from a table in `test.csv` and selecting the first two rows from it:
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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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Getting the first 10 lines of a table that contains 3 columns of [UInt32](/docs/en/sql-reference/data-types/int-uint.md) type from a CSV file:
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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 10;
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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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## Globs in Path
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Multiple path components can have globs. For being processed file must exist and match to the whole path pattern (not only suffix or prefix).
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- `*` — Substitutes any number of any characters except `/` including empty string.
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- `?` — Substitutes any single character.
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- `{some_string,another_string,yet_another_one}` — Substitutes any of strings `'some_string', 'another_string', 'yet_another_one'`.
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- `{N..M}` — Substitutes any number in range from N to M including both borders.
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- `**` - Fetches all files inside the folder recursively.
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Constructions with `{}` are similar to the [remote](remote.md) table function.
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**Example**
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Suppose we have several 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 number of rows in these 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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Query the number of rows in all files of these two directories:
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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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:::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 data from 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 data from all files inside `big_dir` directory 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 data from all `file002` files from any folder inside `big_dir` directory 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
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- `_path` — Path to the file.
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- `_file` — Name of the file.
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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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