SqlDust just got a level up! As of version 0.1.1, it is possible to compose queries based on Ecto models:

import Ecto.SqlDust

City
  |> select("id, name, country.name, local_weather.temp_lo")
  |> where("local_weather.wdate = '2015-09-12'")
  |> to_sql

SELECT
  "c".id,
  "c".name,
  "country".name,
  "local_weather".temp_lo,
  "local_weather".temp_hi
FROM cities "c"
LEFT JOIN countries "country" ON "country".id = "c".country_id
LEFT JOIN weather "local_weather" ON "local_weather".city_id = "c".id
WHERE ("local_weather".wdate = '2015-09-12')

https://github.com/archan937/sql_dust#composable-queries-using-ecto-models