added file() write to docs
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/en/sql-reference/table-functions/file | 37 | file |
file
Provides a table-like interface to SELECT from and INSERT to files. This table function is similar to the s3 table function. Use file() when working with local files, and s3() when working with buckets in S3, GCS, or MinIO.
The file
function can be used in SELECT
and INSERT
queries to read from or write to files.
Syntax
file(path [,format] [,structure] [,compression])
Parameters
path
— The relative path to the file from user_files_path. Path to file support following globs in read-only mode:*
,?
,{abc,def}
and{N..M}
whereN
,M
— numbers,'abc', 'def'
— strings.format
— The format of the file.structure
— Structure of the table. Format:'column1_name column1_type, column2_name column2_type, ...'
.compression
— The existing compression type when used in aSELECT
query, or the desired compression type when used in anINSERT
query. The supported compression types aregz
,br
,xz
,zst
,lz4
, andbz2
.
Returned value
A table with the specified structure for reading or writing data in the specified file.
File Write Examples
Write to a TSV file
INSERT INTO TABLE FUNCTION
file('test.tsv', 'TSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
VALUES (1, 2, 3), (3, 2, 1), (1, 3, 2)
As a result, the data is written into the file test.tsv
:
# cat /var/lib/clickhouse/user_files/test.tsv
1 2 3
3 2 1
1 3 2
Partitioned Write to multiple TSV files
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.
INSERT INTO TABLE FUNCTION
file('test_{_partition_id}.tsv', 'TSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
PARTITION BY column3
VALUES (1, 2, 3), (3, 2, 1), (1, 3, 2)
As a result, the data is written into three files: test_1.tsv
, test_2.tsv
, and test_3.tsv
.
# cat /var/lib/clickhouse/user_files/test_1.tsv
3 2 1
# cat /var/lib/clickhouse/user_files/test_2.tsv
1 3 2
# cat /var/lib/clickhouse/user_files/test_3.tsv
1 2 3
File Read Examples
SELECT from a CSV file
Setting user_files_path
and the contents of the file test.csv
:
$ grep user_files_path /etc/clickhouse-server/config.xml
<user_files_path>/var/lib/clickhouse/user_files/</user_files_path>
$ cat /var/lib/clickhouse/user_files/test.csv
1,2,3
3,2,1
78,43,45
Getting data from a table in test.csv
and selecting the first two rows from it:
SELECT * FROM
file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
LIMIT 2;
┌─column1─┬─column2─┬─column3─┐
│ 1 │ 2 │ 3 │
│ 3 │ 2 │ 1 │
└─────────┴─────────┴─────────┘
Getting the first 10 lines of a table that contains 3 columns of UInt32 type from a CSV file:
SELECT * FROM
file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
LIMIT 10;
Inserting data from a file into a table:
INSERT INTO FUNCTION
file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
VALUES (1, 2, 3), (3, 2, 1);
SELECT * FROM
file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32');
┌─column1─┬─column2─┬─column3─┐
│ 1 │ 2 │ 3 │
│ 3 │ 2 │ 1 │
└─────────┴─────────┴─────────┘
Globs in Path
Multiple path components can have globs. For being processed file must exist and match to the whole path pattern (not only suffix or prefix).
*
— Substitutes any number of any characters except/
including empty string.?
— Substitutes any single character.{some_string,another_string,yet_another_one}
— Substitutes any of strings'some_string', 'another_string', 'yet_another_one'
.{N..M}
— Substitutes any number in range from N to M including both borders.**
- Fetches all files inside the folder recursively.
Constructions with {}
are similar to the remote table function.
Example
Suppose we have several files with the following relative paths:
- 'some_dir/some_file_1'
- 'some_dir/some_file_2'
- 'some_dir/some_file_3'
- 'another_dir/some_file_1'
- 'another_dir/some_file_2'
- 'another_dir/some_file_3'
Query the number of rows in these files:
SELECT count(*) FROM file('{some,another}_dir/some_file_{1..3}', 'TSV', 'name String, value UInt32');
Query the number of rows in all files of these two directories:
SELECT count(*) FROM file('{some,another}_dir/*', 'TSV', 'name String, value UInt32');
:::note
If your listing of files contains number ranges with leading zeros, use the construction with braces for each digit separately or use ?
.
:::
Example
Query the data from files named file000
, file001
, … , file999
:
SELECT count(*) FROM file('big_dir/file{0..9}{0..9}{0..9}', 'CSV', 'name String, value UInt32');
Example
Query the data from all files inside big_dir
directory recursively:
SELECT count(*) FROM file('big_dir/**', 'CSV', 'name String, value UInt32');
Example
Query the data from all file002
files from any folder inside big_dir
directory recursively:
SELECT count(*) FROM file('big_dir/**/file002', 'CSV', 'name String, value UInt32');
Virtual Columns
_path
— Path to the file._file
— Name of the file.
See Also