> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-postgresql-tls-support.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# Как преобразовать файлы из Parquet в CSV или JSON?
> Узнайте, как с помощью инструмента ClickHouse `clickhouse-local` легко преобразовать файлы Parquet в форматы CSV или JSON.
{frontMatter.description}
## Преобразование файлов из Parquet в CSV или JSON
Вы можете использовать `clickhouse-local` для преобразования файлов между любыми [входными и выходными форматами](/ru/reference/formats/index), которые поддерживает ClickHouse (а это более 70 различных форматов!). В этой статье мы преобразуем файл Parquet из S3 в CSV- и JSON‑файл.
Начнём с самого начала. В ClickHouse есть набор [табличных функций](/ru/reference/functions/table-functions/index), которые читают данные из файлов, баз данных и других ресурсов и представляют их в виде таблицы. Для примера предположим, что у нас есть файл Parquet в S3. Мы будем использовать табличную функцию `s3`, чтобы прочитать его (ClickHouse определяет, что это файл Parquet, по имени файла).
Но сначала давайте загрузим бинарный файл `clickhouse`:
```bash theme={null}
curl https://clickhouse.com/ | sh
```
## Доступ к данным с помощью табличной функции
Давайте убедимся, что файл можно прочитать, выполнив `DESCRIBE` для результирующей таблицы, которую создаёт табличная функция `s3`:
```bash theme={null}
./clickhouse local -q "DESCRIBE s3('https://datasets-documentation.s3.eu-west-3.amazonaws.com/house_parquet/house_0.parquet')"
```
Этот файл содержит цены на жильё объектов недвижимости, проданных в Соединённом Королевстве. Ответ выглядит так:
```response theme={null}
price Nullable(Int64)
date Nullable(UInt16)
postcode1 Nullable(String)
postcode2 Nullable(String)
type Nullable(String)
is_new Nullable(UInt8)
duration Nullable(String)
addr1 Nullable(String)
addr2 Nullable(String)
street Nullable(String)
locality Nullable(String)
town Nullable(String)
district Nullable(String)
county Nullable(String)
```
Вы можете выполнить любой запрос к данным. Например, давайте посмотрим, в каких городах самая высокая средняя цена на жилье:
```bash theme={null}
./clickhouse local -q "SELECT
town,
avg(price) AS avg_price
FROM s3('https://datasets-documentation.s3.eu-west-3.amazonaws.com/house_parquet/house_0.parquet')
GROUP BY town
ORDER BY avg_price DESC
LIMIT 10"
```
Ответ будет выглядеть так:
```bash theme={null}
GATWICK 16818750
CHALFONT ST GILES 938090.0985915493
VIRGINIA WATER 789301.1320224719
COBHAM 699874.7111622555
BEACONSFIELD 677247.5483146068
ESHER 616004.6888297872
KESTON 607585.8597560975
GERRARDS CROSS 566330.2959086584
ASCOT 551491.2975753123
WEYBRIDGE 548974.828692494
```
## Преобразование файла Parquet в CSV
Результат любого SQL-запроса можно записать в файл. Давайте извлечём все столбцы из нашего файла Parquet в S3 и запишем результат в новый CSV-файл. Поскольку имя выходного файла оканчивается на `.csv`, ClickHouse понимает, что нужно использовать выходной формат `CSV`:
```bash theme={null}
./clickhouse local -q "SELECT *
FROM s3('https://datasets-documentation.s3.eu-west-3.amazonaws.com/house_parquet/house_0.parquet')
INTO OUTFILE 'house_prices.csv'"
```
Проверим, что всё сработало:
```response theme={null}
$ tail house_prices.csv
70000,10508,"YO8","9XN","detached",0,"freehold","7","","POPPY CLOSE","SELBY","SELBY","SELBY","NORTH YORKSHIRE"
130000,14274,"YO8","9XP","detached",0,"freehold","10","","HEATHER CLOSE","","SELBY","SELBY","NORTH YORKSHIRE"
150000,18180,"YO8","9XP","detached",0,"freehold","11","","HEATHER CLOSE","","SELBY","SELBY","NORTH YORKSHIRE"
157000,18088,"YO8","9XP","detached",0,"freehold","12","","HEATHER CLOSE","","SELBY","SELBY","NORTH YORKSHIRE"
134000,17333,"YO8","9XP","semi-detached",0,"freehold","16","","HEATHER CLOSE","","SELBY","SELBY","NORTH YORKSHIRE"
250000,13405,"YO8","9YA","detached",0,"freehold","6","","YORKDALE COURT","HAMBLETON","SELBY","SELBY","NORTH YORKSHIRE"
59500,11166,"YO8","9YB","semi-detached",0,"freehold","4","","YORKDALE DRIVE","HAMBLETON","SELBY","SELBY","NORTH YORKSHIRE"
142500,17648,"YO8","9YB","semi-detached",0,"freehold","4A","","YORKDALE DRIVE","HAMBLETON","SELBY","SELBY","NORTH YORKSHIRE"
230000,15125,"YO8","9YD","detached",0,"freehold","1","","ONE ACRE GARTH","HAMBLETON","SELBY","SELBY","NORTH YORKSHIRE"
250000,15950,"YO8","9YD","detached",0,"freehold","3","","ONE ACRE GARTH","HAMBLETON","SELBY","SELBY","NORTH YORKSHIRE"
```
## Преобразуйте файл Parquet в JSON
Чтобы преобразовать файл Parquet в JSON, просто измените расширение выходного файла:
```bash theme={null}
./clickhouse local -q "SELECT *
FROM s3('https://datasets-documentation.s3.eu-west-3.amazonaws.com/house_parquet/house_0.parquet')
INTO OUTFILE 'house_prices.ndjson'"
```
Давайте проверим, что всё сработало:
```response theme={null}
$ tail house_prices.ndjson
{"price":"70000","date":10508,"postcode1":"YO8","postcode2":"9XN","type":"detached","is_new":0,"duration":"freehold","addr1":"7","addr2":"","street":"POPPY CLOSE","locality":"SELBY","town":"SELBY","district":"SELBY","county":"NORTH YORKSHIRE"}
{"price":"130000","date":14274,"postcode1":"YO8","postcode2":"9XP","type":"detached","is_new":0,"duration":"freehold","addr1":"10","addr2":"","street":"HEATHER CLOSE","locality":"","town":"SELBY","district":"SELBY","county":"NORTH YORKSHIRE"}
{"price":"150000","date":18180,"postcode1":"YO8","postcode2":"9XP","type":"detached","is_new":0,"duration":"freehold","addr1":"11","addr2":"","street":"HEATHER CLOSE","locality":"","town":"SELBY","district":"SELBY","county":"NORTH YORKSHIRE"}
{"price":"157000","date":18088,"postcode1":"YO8","postcode2":"9XP","type":"detached","is_new":0,"duration":"freehold","addr1":"12","addr2":"","street":"HEATHER CLOSE","locality":"","town":"SELBY","district":"SELBY","county":"NORTH YORKSHIRE"}
{"price":"134000","date":17333,"postcode1":"YO8","postcode2":"9XP","type":"semi-detached","is_new":0,"duration":"freehold","addr1":"16","addr2":"","street":"HEATHER CLOSE","locality":"","town":"SELBY","district":"SELBY","county":"NORTH YORKSHIRE"}
{"price":"250000","date":13405,"postcode1":"YO8","postcode2":"9YA","type":"detached","is_new":0,"duration":"freehold","addr1":"6","addr2":"","street":"YORKDALE COURT","locality":"HAMBLETON","town":"SELBY","district":"SELBY","county":"NORTH YORKSHIRE"}
{"price":"59500","date":11166,"postcode1":"YO8","postcode2":"9YB","type":"semi-detached","is_new":0,"duration":"freehold","addr1":"4","addr2":"","street":"YORKDALE DRIVE","locality":"HAMBLETON","town":"SELBY","district":"SELBY","county":"NORTH YORKSHIRE"}
{"price":"142500","date":17648,"postcode1":"YO8","postcode2":"9YB","type":"semi-detached","is_new":0,"duration":"freehold","addr1":"4A","addr2":"","street":"YORKDALE DRIVE","locality":"HAMBLETON","town":"SELBY","district":"SELBY","county":"NORTH YORKSHIRE"}
{"price":"230000","date":15125,"postcode1":"YO8","postcode2":"9YD","type":"detached","is_new":0,"duration":"freehold","addr1":"1","addr2":"","street":"ONE ACRE GARTH","locality":"HAMBLETON","town":"SELBY","district":"SELBY","county":"NORTH YORKSHIRE"}
{"price":"250000","date":15950,"postcode1":"YO8","postcode2":"9YD","type":"detached","is_new":0,"duration":"freehold","addr1":"3","addr2":"","street":"ONE ACRE GARTH","locality":"HAMBLETON","town":"SELBY","district":"SELBY","county":"NORTH YORKSHIRE"}
```
## Преобразование CSV в Parquet
Это работает в обе стороны: мы можем без труда прочитать новый CSV-файл и записать его в файл Parquet. Локальный файл `house_prices.csv` можно прочитать в ClickHouse с помощью табличной функции `file`, а ClickHouse запишет файл в формате Parquet на основе расширения имени файла `.parquet` (или можно было бы добавить предложение `FORMAT Parquet`):
```bash theme={null}
./clickhouse local -q "SELECT *
FROM file('house_prices.csv')
INTO OUTFILE 'house_prices.parquet'"
```
Как уже упоминалось выше, вы можете использовать любой из [форматов ввода и вывода ClickHouse](/ru/reference/formats/index) вместе с `clickhouse local`, чтобы легко преобразовывать файлы в разные форматы.