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    Parquet To Csv Json

    How do I convert Files from Parquet to CSV or JSON?

    Learn how to use ClickHouse's `clickhouse-local` tool to easily convert Parquet files to CSV or JSON formats.

    Converting Files from Parquet to CSV or JSON​

    You can use clickhouse-local to convert files between any of the input and output formats that ClickHouse supports (which is over 70 different formats!). In this article, we are convert a Parquet file in S3 into a CSV and JSON file.

    Let's start at the beginning. ClickHouse has a collection of table functions that read from files, databases and other resoures and converts the data to a table. To demonstrate, suppose we have a Parquet file in S3. We will use the s3 table function to read it (ClickHouse knows it's a Parquet file based on the filename).

    But first, let's download the clickhouse binary:

    Accessing the data using a table function​

    Let's verify we can read the file by using DESCRIBE on the resulting table that the s3 table function creates:

    This particular file contains home prices of properties sold in the United Kingdom. The response looks like:

    You can run any query you want on the data. For example, let's see which towns have the highest average price of homes:

    The response looks like:

    Convert the Parquet file to a CSV​

    You can send the result of any SQL query to a file. Let's grab all the columns from our Parquet file in S3 and send the output to a new CSV file. Because the output file ends in .csv, ClickHouse knows to use the CSV output format:

    Let's verify it worked:

    Convert the Parquet file to a JSON​

    To convert the Parquet file to JSON, simply change the extension on the output filename:

    Let's verify it worked:

    Convert CSV to Parquet​

    It works both ways - we can easily read in the new CSV file and output it into a Parquet file. The local file house_prices.csv can be read in ClickHouse using the file table function, and ClickHouse outputs the file in Parquet format based on the filename ending in .parquet (or we could have added the FORMAT Parquet clause):

    As we mentioned above, you can use any of the ClickHouse input and output formats along with clickhouse local to easily convert files into different formats.

    · 3 min read