Good news! Many database systems support indexes on functions, including on user-defined functions. The only one I've used is Postgres[0] but apparently MySQL added support recently as well[1]
That's cool, but then I'd assume you have to make an index for each function.
In general if a person is asking basic questions about sargability, I will steer them away from functions on a predicate (it's usually my last choice.)
Often you can just think a bit harder about your set based logic and make an index that's reusable by other queries.
In other SQL's you can also make a materialized view, which may be able to persist some of these things, its just like keeping n+1 copies of your data to satisfy a different set of relations/projections.
Often you can just think a bit harder about your set based logic and make an index that's reusable by other queries.
In other SQL's you can also make a materialized view, which may be able to persist some of these things, its just like keeping n+1 copies of your data to satisfy a different set of relations/projections.