How to create Cosmos DB federated tables in MySQL

You can use the SQL Gateway to configure a MySQL remoting service and set up federated tables for Cosmos DB data. The service is a daemon process that provides a MySQL interface to the CData ODBC Driver for Cosmos DB: After you have started the service, you can create a server and tables using the FEDERATED Storage Engine in MySQL. You can then work with Cosmos DB data just as you would local MySQL tables.

Connect to Cosmos DB Data

If you have not already done so, provide values for the required connection properties in the data source name (DSN). You can use the built-in Microsoft ODBC Data Source Administrator to configure the DSN. This is also the last step of the driver installation. See the "Getting Started" chapter in the help documentation for a guide to using the Microsoft ODBC Data Source Administrator to create and configure a DSN.

To obtain the connection string needed to connect to a Cosmos DB account using the SQL API, log in to the Azure Portal, select Azure Cosmos DB, and select your account. In the Settings section, click Connection String and set the following values:

• AccountEndpoint: The Cosmos DB account URL from the Keys blade of the Cosmos DB account
• AccountKey: In the Azure portal, navigate to the Cosmos DB service and select your Azure Cosmos DB account. From the resource menu, go to the Keys page. Find the PRIMARY KEY value and set AccountKey to this value.

Configure the SQL Gateway

See the SQL Gateway Overview to set up connectivity to Cosmos DB data as a virtual MySQL database. You will configure a MySQL remoting service that listens for MySQL requests from clients. The service can be configured in the SQL Gateway UI.

Create a FEDERATED Server and Tables for Cosmos DB Data

After you have configured and started the service, create a FEDERATED server to simplify the process of creating FEDERATED tables:

Create a FEDERATED Server

The following statement will create a FEDERATED server based on the ODBC Driver for Cosmos DB. Note that the username and password of the FEDERATED server must match a user account you defined on the Users tab of the SQL Gateway.

CREATE SERVER fedCosmosDB
FOREIGN DATA WRAPPER mysql
OPTIONS (USER 'sql_gateway_user', PASSWORD 'sql_gateway_passwd', HOST 'sql_gateway_host', PORT ####, DATABASE 'CData CosmosDB Sys');

Create a FEDERATED Table

To create a FEDERATED table using our newly created server, use the CONNECTION keyword and pass the name of the FEDERATED server and the remote table (Customers). Refer to the following template for the statement to create a FEDERATED table:

CREATE TABLE fed_customers (
  ...,
  city  TYPE(LEN),
  companyname  TYPE(LEN),
  ...,
)
ENGINE=FEDERATED
DEFAULT CHARSET=latin1
CONNECTION='fedCosmosDB/customers';

NOTE: The table schema for the FEDERATED table must match the remote table schema exactly. You can always connect directly to the MySQL remoting service using any MySQL client and run a SHOW CREATE TABLE query to get the table schema.

Execute Queries

You can now execute queries to the Cosmos DB FEDERATED tables from any tool that can connect to MySQL, which is particularly useful if you need to JOIN data from a local table with data from Cosmos DB. Refer to the following example:

SELECT 
  fed_customers.city, 
  local_table.custom_field 
FROM 
  local_table 
JOIN 
  fed_customers 
ON 
  local_table.foreign_city = fed_customers.city;