What is ISBN UK, when Author is "Dave Martin", and when ISBN US is "N/A"?
CREATE TABLE "game_books" (
  "title" text,
  "author" text,
  "isbn_uk" text,
  "isbn_us" text,
  "tv_companions_featured" text
);
SELECT "isbn_uk" FROM "game_books" WHERE "author"='dave martin' AND "isbn_us"='n/a';