New table in pihole-FTL.db, similar to gravity.db info table with database version field.
A lot of users are writing custom SQL scripts, to extract and display (or update) data from the database in a format, not provided in the web interface.
Given the new field in pihole-FTL.db, table queries, field additional_info, which can be used to store any kind of information, it would be useful to check the database version, before displaying or updating database entries.
I agree with you that versioning for pihole itself might not be of any value, because the script will (should) be always in concordance with the ability the database provides.
But I see the benefit for users attaching own scripts/code to the database. They would benefit from an easy version string which would let them know the capabilities of the current database they interact with.
I was just going to say exactly this. Looking into the file @yubiuser linked, there is an entire chain of updates to ensure you can update any version of Pi-hole to a newer one (not only 5.1 -> 5.2 but also 4.0 -> 5.2, etc.).
Actually a lot changed (like allowing multiple host names per client by moving them from per-MAC address to per-IP address basis, etc.)
The current version with v5.2 is 7
The version after having merged new/super-clients will be 9: