CREATE TABLE "season_by_season" (
  "season" text,
  "tier" real,
  "league" text,
  "pos" real,
  "postseason" text,
  "european_competitions" text
);

Question: What is the total number of tiers for the postseason of semifinalist?
SQL: SELECT SUM("tier") FROM "season_by_season" WHERE "postseason"='semifinalist';