CREATE TABLE "season_4" (
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text
);

Question: tell me the writer of production code ad1d09.
SQL: SELECT "written_by" FROM "season_4" WHERE "production_code"='ad1d09';

Question: tell me the director of the production code ad1d02.
SQL: SELECT "directed_by" FROM "season_4" WHERE "production_code"='ad1d02';