CREATE TABLE "table1_12159115_2" (
  "series_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_millions" text
);

Question: What's the original air date of the episode with production code 2T6719?
SQL: SELECT "original_air_date" FROM "table1_12159115_2" WHERE "production_code"='2T6719';

Question: Who's the writer of the episode see by 12.13 million US viewers?
SQL: SELECT "written_by" FROM "table1_12159115_2" WHERE "u_s_viewers_millions"='12.13';

Question: What's the total number of episodes with production code 2T6705?
SQL: SELECT COUNT("title") FROM "table1_12159115_2" WHERE "production_code"='2T6705';

Question: What's the total number of directors who've directed episodes seen by 11.34 million US viewers?
SQL: SELECT COUNT("directed_by") FROM "table1_12159115_2" WHERE "u_s_viewers_millions"='11.34';

Question: What's the production code of the episode seen by 11.64 million US viewers?
SQL: SELECT "production_code" FROM "table1_12159115_2" WHERE "u_s_viewers_millions"='11.64';