Are there Sql backends that return an array from big_query()?

I think the architecture is outdated, so instead it would be more
valuable to look at how to make it properly. Instead of having a proxy
object that calls a database object, there should be inheritance that
allows direct calling when possible.

Something like this

Database get_db(string url)
{
  // parse, lookup and clone a database object, e.g. MySql below.
}

class MySql
{

  // Contains the different APIs (query/typed_query/big_query) and
  // convenience functions.
  inherit Database;

  // Contains the actual implementations. Can replace any or all of
  // the methods of Database.
  inherit _Mysql;
}