How Can I Query Multiple WordPress Databases for the Same Data in a Single SQL Query?

Retrieving Data from Multiple Databases in a Single Query

Suppose you have multiple WordPress databases and need to consolidate data, such as active plugins, from all of them. Each database contains its own table ('wp_options') with the plugin data stored in the 'active_plugins' column. To access all these values simultaneously, you can utilize SQL's UNION operator.

To elaborate on the provided question, you want to query the 'wp_options' table for the 'active_plugins' value in every database. Typically, a query would look like this:

SELECT option_value
FROM `database`.`wp_options`
WHERE option_name="active_plugins"

To query multiple databases, you can use the following structure:

SELECT option_value
FROM `database1`.`wp_options`
WHERE option_name="active_plugins"
UNION
SELECT option_value
FROM `database2`.`wp_options`
WHERE option_name="active_plugins"

The UNION operator combines the results of the individual queries into a single result set. Each subquery remains separate, resulting in multiple rows in the output if there are common values among the databases.

By combining the database.tablename syntax with the UNION operator, you can efficiently retrieve data from multiple databases and consolidate it into a single result, streamlining your update process.

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