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文件

从文件创建表。 此表函数类似于 url 和 hdfs 一些的。

  1. file(path, format, structure)

输入参数

  • path — The relative path to the file from user_files_path. 只读模式下的globs后的文件支持路径: *, ?, {abc,def} 和 {N..M} 哪里 N, M — numbers, `'abc', 'def' — strings.
  • format — The 格式 的文件。
  • structure — Structure of the table. Format 'column1_name column1_type, column2_name column2_type, ...'.

返回值

具有指定结构的表，用于读取或写入指定文件中的数据。

示例

设置 user_files_path 和文件的内容 test.csv:

  1. $ grep user_files_path /etc/clickhouse-server/config.xml
  2.     <user_files_path>/var/lib/clickhouse/user_files/</user_files_path>
  4. $ cat /var/lib/clickhouse/user_files/test.csv
  5.     1,2,3
  6.     3,2,1
  7.     78,43,45

表从test.csv 并从中选择前两行:

  1. SELECT *
  2. FROM file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
  3. LIMIT 2
  1. ┌─column1─┬─column2─┬─column3─┐
  2. │       1 │       2 │       3 │
  3. │       3 │       2 │       1 │
  4. └─────────┴─────────┴─────────┘
  1. -- getting the first 10 lines of a table that contains 3 columns of UInt32 type from a CSV file
  2. SELECT * FROM file('test.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32') LIMIT 10

路径中的水珠

多个路径组件可以具有globs。 对于正在处理的文件应该存在并匹配到整个路径模式（不仅后缀或前缀）。

  • * — Substitutes any number of any characters except / 包括空字符串。
  • ? — 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.

建筑与 {} 类似于 远程表功能).

示例

  1. 假设我们有几个具有以下相对路径的文件:
  • ‘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. 查询这些文件中的行数:
  1. SELECT count(*)
  2. FROM file('{some,another}_dir/some_file_{1..3}', 'TSV', 'name String, value UInt32')
  1. 查询这两个目录的所有文件中的行数:
  1. SELECT count(*)
  2. FROM file('{some,another}_dir/*', 'TSV', 'name String, value UInt32')

警告

如果您的文件列表包含带前导零的数字范围，请单独使用带大括号的构造或使用 ?.

示例

从名为 file000, file001, … , file999:

  1. SELECT count(*)
  2. FROM file('big_dir/file{0..9}{0..9}{0..9}', 'CSV', 'name String, value UInt32')

虚拟列

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

另请参阅

原始文章