From the sample on the front page

  SELECT "c"."id"
  FROM "Customer" "c"
    LEFT JOIN "Order" "order-1"
      ON "c"."id" = "order-1"."customer"
  GROUP BY "c"."id"
  HAVING coalesce(SUM("order-1"."total_price"), 0) > 1000

is translated into

  select(c for c in Customer
           if sum(c.orders.price) > 1000)

How does the python version handle nulls? They are explicitly coalesced into 0s in SQL. In python sum([1,numpy.NaN]) evaluates to nan. I think this code will do something wrong.

I am not sure what flavor of SQL is beind used, but why are the table names and the field names surrounded by double quotes? They make the query look unnecesierily hairy.

Good job otherwise. Always glad to see people contributing to the community.