JRjrockway·May 23, 2022
You could do that in Go, but it's not what database/sql's API supports. You read columns out of each row with "row.Scan(&col1, &col2, ...)". The types of col1 and col2 are declared at compile time, and they don't have to be able to represent the concept of null. So there would be no way to store the state that represents that something was null.
You could of course have an API that just returns a slice of "any", and conditionally check whether a value is of type "string" or "mylibrary.NullValue" after the fact. This isn't clearly better to me than the Scan API. You are going to have to eventually cast "any" to a real type in order to use it; with Scan the library does that for you.
Your own types can implement sql.Scanner to control exactly how you want to handle something. (Indeed, your "Scan" method receives something with type "a
Read the rest
ny", and you need to check what the type is and convert it to your internal representation.)
Also wanted to throw this out here; you don't have to be satisfied with lossy versions of your database's built in types. Libraries like https://pkg.go.dev/github.com/jackc/pgtype@v1.11.0 will give you a 1:1 mapping to Postgres's types. (I'm sure other database systems have similar libraries.)