In a WordPress multisite network, all sites share the same database but use different tables to store their data. Each subsite has its own set of tables with a unique prefix, allowing them to maintain separate content and settings while still being part of the same database. For example, the tables for a subsite with ID 2 would be prefixed with `wp_2_` (e.g., `wp_2_posts`, `wp_2_options`) [2][3].
However, you cannot use different database versions for different sites within the same multisite network. The entire network operates on a single version of the database structure, which means that all sites must adhere to the same database schema and version. This ensures consistency and compatibility across the network, as changes to the database structure would affect all sites simultaneously [1][3].
If you need to manage different versions of a database for various sites, you would have to set up separate WordPress installations instead of using a multisite configuration. In a multisite setup, the design is inherently meant to keep the sites interconnected under a unified database structure, making it impractical to run different database versions concurrently.
Citations:[1] https://wordpress.stackexchange.com/questions/333142/how-to-have-differents-sites-share-the-same-tables-of-db
[2] https://docs.wpvip.com/wordpress-on-vip/multisites/database-structure/
[3] https://kinsta.com/blog/wordpress-multisite/
[4] https://dev.to/4sushi/how-to-handle-database-versions-on-multiple-environments-f93
[5] https://athemeart.com/blog/multisite-network-wordpress/