MySQL: Inter-Database Joins on Remote Servers From Python

Challenge: Perform database joins between two MySQL databases residing on different servers using Python's MySQLDB.

Solution:

To establish connections to the two databases, create MySQLDB connections for each server using separate connection parameters. However, the subsequent join operation cannot be directly performed using MySQLDB as it lacks cross-server join functionality.

Alternative Approaches:

FEDERATED Storage Engine:
MySQL offers the FEDERATED storage engine, allowing you to access tables from remote databases as if they were local. Use the following syntax to create a federated table:

CREATE FEDERATED TABLE remote_table (
  column_1 data_type,
  column_2 data_type,
  ...
) ENGINE=FEDERATED
CONNECTION='mysql://username:password@server2/database_B';

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Linked Servers Workaround:

If using MySQL is not feasible, you can utilize another DBMS that supports linked servers, such as Microsoft SQL Server. Here, you can create a linked server to connect to database A from database B and perform the join using queries within the middleware DBMS.

Implementation in Python:

Depending on your chosen approach:

FEDERATED Engine:

import MySQLdb

# Create a connection to the local database
conn_local = MySQLdb.connect(...)

# Create a cursor for the local connection
cursor_local = conn_local.cursor()

# Execute a query to join the local table with the remote table
cursor_local.execute("""
  SELECT *
  FROM local_table
  INNER JOIN remote_table
  ON local_table.id = remote_table.id
""")

result = cursor_local.fetchall()

**Linked Servers Workaround:**

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import pymssql

Establish a connection to the external DBMS

conn_external = pymssql.connect(...)

Execute a query to retrieve data from both databases

cursor_external.execute("""
SELECT *
FROM linked_server_A.database_A.dbo.local_table
INNER JOIN linked_server_B.database_B.dbo.remote_table
ON linked_server_A.database_A.dbo.local_table.id = linked_server_B.database_B.dbo.remote_table.id
""")

result = cursor_external.fetchall()

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