What is the weeks rank for the episode with the production code 1alf05? 
CREATE TABLE "table1_26198709_1" (
  "no" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "u_s_viewers_million" text,
  "rank_week" real,
  "original_air_date" text,
  "production_code" text
);
SELECT MAX("rank_week") FROM "table1_26198709_1" WHERE "production_code"='1ALF05';