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105 lines
3.5 KiB
Markdown
105 lines
3.5 KiB
Markdown
---
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machine_translated: true
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machine_translated_rev: 72537a2d527c63c07aa5d2361a8829f3895cf2bd
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toc_priority: 45
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toc_title: Hdfs
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---
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# Hdfs {#hdfs}
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Crea una tabla a partir de archivos en HDFS. Esta función de tabla es similar a [URL](url.md) y [file](file.md) aquel.
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``` sql
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hdfs(URI, format, structure)
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```
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**Parámetros de entrada**
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- `URI` — The relative URI to the file in HDFS. Path to file support following globs in readonly mode: `*`, `?`, `{abc,def}` y `{N..M}` donde `N`, `M` — numbers, \``'abc', 'def'` — strings.
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- `format` — The [formato](../../interfaces/formats.md#formats) del archivo.
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- `structure` — Structure of the table. Format `'column1_name column1_type, column2_name column2_type, ...'`.
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**Valor devuelto**
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Una tabla con la estructura especificada para leer o escribir datos en el archivo especificado.
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**Ejemplo**
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Tabla de `hdfs://hdfs1:9000/test` y selección de las dos primeras filas de ella:
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``` sql
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SELECT *
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FROM hdfs('hdfs://hdfs1:9000/test', 'TSV', '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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**Globs en el camino**
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Múltiples componentes de ruta de acceso pueden tener globs. Para ser procesado, el archivo debe existir y coincidir con todo el patrón de ruta (no solo el sufijo o el prefijo).
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- `*` — Substitutes any number of any characters except `/` incluyendo cadena vacía.
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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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Construcciones con `{}` son similares a la [función de tabla remota](../../sql-reference/table-functions/remote.md)).
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**Ejemplo**
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1. Supongamos que tenemos varios archivos con los siguientes URI en HDFS:
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- ‘hdfs://hdfs1:9000/some\_dir/some\_file\_1’
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- ‘hdfs://hdfs1:9000/some\_dir/some\_file\_2’
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- ‘hdfs://hdfs1:9000/some\_dir/some\_file\_3’
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- ‘hdfs://hdfs1:9000/another\_dir/some\_file\_1’
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- ‘hdfs://hdfs1:9000/another\_dir/some\_file\_2’
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- ‘hdfs://hdfs1:9000/another\_dir/some\_file\_3’
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1. Consulta la cantidad de filas en estos archivos:
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<!-- -->
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``` sql
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SELECT count(*)
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FROM hdfs('hdfs://hdfs1:9000/{some,another}_dir/some_file_{1..3}', 'TSV', 'name String, value UInt32')
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```
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1. Consulta la cantidad de filas en todos los archivos de estos dos directorios:
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<!-- -->
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``` sql
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SELECT count(*)
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FROM hdfs('hdfs://hdfs1:9000/{some,another}_dir/*', 'TSV', 'name String, value UInt32')
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```
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!!! warning "Advertencia"
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Si su lista de archivos contiene rangos de números con ceros a la izquierda, use la construcción con llaves para cada dígito por separado o use `?`.
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**Ejemplo**
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Consultar los datos desde archivos nombrados `file000`, `file001`, … , `file999`:
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``` sql
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SELECT count(*)
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FROM hdfs('hdfs://hdfs1:9000/big_dir/file{0..9}{0..9}{0..9}', 'CSV', 'name String, value UInt32')
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```
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## Virtual Columnas {#virtual-columns}
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- `_path` — Path to the file.
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- `_file` — Name of the file.
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**Ver también**
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- [Virtual columnas](https://clickhouse.tech/docs/en/operations/table_engines/#table_engines-virtual_columns)
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[Artículo Original](https://clickhouse.tech/docs/en/query_language/table_functions/hdfs/) <!--hide-->
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