What is the average last yr with an l plyf less than 0?
CREATE TABLE "coaches" (
  "coach" text,
  "first_yr" real,
  "last_yr" real,
  "w_lpct" real,
  "g_500" real,
  "yr_plyf" real,
  "g_plyf" real,
  "w_plyf" real,
  "l_plyf" real
);
SELECT AVG("last_yr") FROM "coaches" WHERE "l_plyf"<0;