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Store query results to storage using serverless SQL pool in Azure Synapse Analytics

  • บทความ

In this article, you'll learn how to store query results to storage using serverless SQL pool.

Prerequisites

Your first step is to create a database where you will execute the queries. Then initialize the objects by executing setup script on that database. This setup script will create the data sources, database scoped credentials, and external file formats that are used to read data in these samples.

Follow the instructions in this article to create data sources, database scoped credentials, and external file formats that are used to write data into the output storage.

Create external table as select

You can use the CREATE EXTERNAL TABLE AS SELECT (CETAS) statement to store the query results to storage.

Note

Change the first line in the query, i.e., [mydbname], so you're using the database you created.

USE [mydbname];
GO

CREATE DATABASE SCOPED CREDENTIAL [SasTokenWrite]
WITH IDENTITY = 'SHARED ACCESS SIGNATURE',
     SECRET = 'sv=2018-03-28&ss=bfqt&srt=sco&sp=rwdlacup&se=2019-04-18T20:42:12Z&st=2019-04-18T12:42:12Z&spr=https&sig=lQHczNvrk1KoYLCpFdSsMANd0ef9BrIPBNJ3VYEIq78%3D';
GO

CREATE EXTERNAL DATA SOURCE [MyDataSource] WITH (
    LOCATION = 'https://<storage account name>.blob.core.windows.net/csv', CREDENTIAL = [SasTokenWrite]
);
GO

CREATE EXTERNAL FILE FORMAT [ParquetFF] WITH (
    FORMAT_TYPE = PARQUET,
    DATA_COMPRESSION = 'org.apache.hadoop.io.compress.SnappyCodec'
);
GO

CREATE EXTERNAL TABLE [dbo].[PopulationCETAS] WITH (
        LOCATION = 'populationParquet/',
        DATA_SOURCE = [MyDataSource],
        FILE_FORMAT = [ParquetFF]
) AS
SELECT
    *
FROM
    OPENROWSET(
        BULK 'csv/population-unix/population.csv',
        DATA_SOURCE = 'sqlondemanddemo',
        FORMAT = 'CSV', PARSER_VERSION = '2.0'
    ) WITH (
        CountryCode varchar(4),
        CountryName varchar(64),
        Year int,
        PopulationCount int
    ) AS r;

Note

You must modify this script and change the target location to execute it again. External tables cannot be created on the location where you already have some data.

Use the external table

You can use the external table created through CETAS like a regular external table.

Note

Change the first line in the query, i.e., [mydbname], so you're using the database you created.

USE [mydbname];
GO

SELECT
    CountryName, PopulationCount
FROM PopulationCETAS
WHERE
    [Year] = 2019
ORDER BY
    [PopulationCount] DESC;

Remarks

Once you store your results, the data in the external table cannot be modified. You cannot repeat this script because CETAS will not overwrite the underlying data created in the previous execution. Vote for the following feedback items if some of these are required in your scenarios, or propose the new ones on Azure feedback site:

The only supported output types are Parquet and CSV. You can vote for the other types on Azure feedback site.

Next steps

For more information on how to query different file types, see the Query single CSV file, Query Parquet files, and Query JSON files articles.