https://www.postgresql.org/docs/current/indexes-expressional.html
PostgreSQL: Documentation: 18: 11.7. Indexes on Expressions
11.7. Indexes on Expressions # An index column need not be just a column of the underlying table, but can be …
indexes on expressionspostgresqldocumentation
https://sqlite.org/expridx.html
Indexes On Expressions
indexes on expressions