CREATE TABLE "table1_20967430_4" (
  "ep" real,
  "season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "prod_code" text
);

Question: Who directed the episode that originally aired on March 18, 1988?
SQL: SELECT "directed_by" FROM "table1_20967430_4" WHERE "original_air_date"='March 18, 1988';

Question: What is the episode number in the series for "graduation" that was directed by Don Corvan?
SQL: SELECT MIN("ep") FROM "table1_20967430_4" WHERE "directed_by"='Don Corvan' AND "title"='\"Graduation\"';

Question: What was the name of the episode that aired originally on March 11, 1988?
SQL: SELECT "title" FROM "table1_20967430_4" WHERE "original_air_date"='March 11, 1988';

Question: What is the production code of the episode written by Jack Carrerrow?
SQL: SELECT "prod_code" FROM "table1_20967430_4" WHERE "written_by"='Jack Carrerrow';

Question: How many episodes had a production code of 5m13?
SQL: SELECT COUNT("ep") FROM "table1_20967430_4" WHERE "prod_code"='5M13';