Cloud SQL federated queries

As a data analyst, you can query data in Cloud SQL from BigQuery using federated queries.

BigQuery Cloud SQL federation enables BigQuery to query data residing in Cloud SQL in real time, without copying or moving data. Query federation supports both MySQL (2nd generation) and PostgreSQL instances in Cloud SQL.

Alternatively, to replicate data into BigQuery, you can also use Cloud Data Fusion or Datastream. For more about using Cloud Data Fusion, see Replicating data from MySQL to BigQuery.

Before you begin

Query data

To send a federated query to Cloud SQL from a GoogleSQL query, use the EXTERNAL_QUERY function.

Suppose that you store a customer table in BigQuery, while storing a sales table in Cloud SQL, and want to join the two tables in a single query. The following example makes a federated query to a Cloud SQL table named orders and joins the results with a BigQuery table named mydataset.customers.

SELECT c.customer_id, c.name, rq.first_order_date
FROM mydataset.customers AS c
LEFT OUTER JOIN EXTERNAL_QUERY(
  'us.connection_id',
  '''SELECT customer_id, MIN(order_date) AS first_order_date
  FROM orders
  GROUP BY customer_id''') AS rq ON rq.customer_id = c.customer_id
GROUP BY c.customer_id, c.name, rq.first_order_date;

The example query includes 3 parts:

  1. Run the external query SELECT customer_id, MIN(order_date) AS first_order_date FROM orders GROUP BY customer_id in the operational PostgreSQL database to get the first order date for each customer through the EXTERNAL_QUERY() function.
  2. Join the external query result table with the customers table in BigQuery by customer_id.
  3. Select customer information and first order date.

View a Cloud SQL table schema

You can use the EXTERNAL_QUERY() function to query information_schema tables to access database metadata, such as list all tables in the database or show table schema. The following example information_schema queries work in both MySQL and PostgreSQL. You can learn more from MySQL information_schema tables and PostgreSQL information_schema tables.

-- List all tables in a database.
SELECT * FROM EXTERNAL_QUERY("connection_id",
"select * from information_schema.tables;");

-- List all columns in a table.
SELECT * FROM EXTERNAL_QUERY("connection_id",
"select * from information_schema.columns where table_name='x';");

Connection details

The following table shows the Cloud SQL connection properties:

Property name Value Description
name string Name of the connection resource in the format: project_id.location_id.connection_id.
location string Location of the connection, which is the same as the Cloud SQL instance location with the following exceptions: Cloud SQL us-central1 maps to BigQuery US, Cloud SQL europe-west1 maps to BigQuery EU.
friendlyName string A user-friendly display name for the connection.
description string Description of the connection.
cloudSql.type string Can be "POSTGRES" or "MYSQL".
cloudSql.instanceId string Name of the Cloud SQL instance, usually in the format of:

Project-id:location-id:instance-id

You can find the instance ID in the Cloud SQL instance detail page.
cloudSql.database string The Cloud SQL database that you want to connect to.
cloudSql.serviceAccountId string The service account configured to access the Cloud SQL database.

The following table shows the properties for the Cloud SQL instance credential:

Property name Value Description
username string Database username
password string Database password

Troubleshooting

This section helps you troubleshoot issues you might encounter when sending a federated query to Cloud SQL.

Issue: Failed to connect to database server. If you are querying a MySQL database, you might encounter the following error:

Invalid table-valued function EXTERNAL_QUERY Failed to connect to MySQL database. Error: MysqlErrorCode(2013): Lost connection to MySQL server during query.

Alternatively, if you are querying a PostgreSQL database, you might encounter the following error:

Invalid table-valued function EXTERNAL_QUERY Connect to PostgreSQL server failed: server closed the connection unexpectedly This probably means the server terminated abnormally before or while processing the request.
Resolution: Ensure that valid credentials were used and all prerequisites were followed to create the connection for Cloud SQL. Check if the service account that is automatically created when a connection to Cloud SQL is created has the Cloud SQL Client (roles/cloudsql.client) role. The service account is of the following format: service-PROJECT_NUMBER@gcp-sa-bigqueryconnection.iam.gserviceaccount.com. For detailed instructions, see Grant access to the service account.

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