What do you want to change?

            CASE
                WHEN t.amount = 0 THEN null
                ELSE t.price - t.amount
            END AS delta,

This gets typed as an empty interface.

            CASE
                WHEN t.amount = 0 THEN null
                ELSE (t.price - t.amount)::float
            END AS delta,

I get this error cannot scan NULL into *float64

This gets typed as a float64 when what I want is pgtype.Float8. Is there a workaround for this?

What database engines need to be changed?

PostgreSQL

What programming language backends need to be changed?

Go