not-exists-3.exs

import Ecto.Query
...

defmacro store_items_not_exist(store_items_table_name, store_id, item_name) do
  args = [
    "NOT EXISTS (SELECT * FROM #{store_items_table_name} item WHERE item.store_id = ? AND item.name == ?)",
    store_id,
    item_name
  ]

  quote do: fragment(unquote_splicing(args))
end

from(store in Store,
  where: store_items_not_exist("appliances", store.id, "VCR player"),
  where: store_items_not_exist("game_consoles", store.id, "Sega Genesis")
)