How many numbers have sp of 20/1 and a finishing position of fence 19?
CREATE TABLE "competitors_and_betting" (
  "sp" text,
  "number" real,
  "horse" text,
  "age" real,
  "handicap_st_lb" text,
  "jockey" text,
  "trainer" text,
  "owner" text,
  "colours" text,
  "finishing_position" text
);
SELECT COUNT("number") FROM "competitors_and_betting" WHERE "sp"='20/1' AND "finishing_position"='Fence 19';