If the macro can open a connection to a database, query the schema, and use the results to construct/inject types into the source, all at compile time, then yes

If the macro can open a connection to a database, query the schema, and use the results to construct/inject types into the source, all at compile time, then yes. That is basically what Slick's type-checked SQL API is doing in Scala. It sounds like something that might be a practical disaster if you don't have incremental compilation though.