ClickHouse/docs/en/query_language/table_functions/file.md

file

Creates a table from a file. This table function is similar to url and hdfs ones.

file(path, format, structure)

Input parameters

• path — The relative path to the file from user_files_path. Path to file support following globs in readonly mode: *, ?, {abc,def} and {N..M} where N, 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, ...'.

Returned value

A table with the specified structure for reading or writing data in the specified file.

Example

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

Table fromtest.csv and selection of 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

Globs in path

Multiple path components can have globs. For being processed file should exists and matches 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.

Constructions with {} are similar to the remote table function).

Example

1. 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’

1. Query the amount of rows in these files:

SELECT count(*)
FROM file('{some,another}_dir/some_file_{1..3}', 'TSV', 'name String, value UInt32')

1. Query the amount of rows in all files of these two directories:

SELECT count(*)
FROM file('{some,another}_dir/*', 'TSV', 'name String, value UInt32')

!!! warning "Warning" 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')

Virtual Columns

• _path — Path to the file.
• _file — Name of the file.

See Also

• Virtual columns

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