What's the maximum crowd when scg is the ground?
CREATE TABLE "round_19" (
  "home_team" text,
  "home_team_score" text,
  "away_team" text,
  "away_team_score" text,
  "ground" text,
  "crowd" real,
  "date" text,
  "report" text
);
SELECT MAX("crowd") FROM "round_19" WHERE "ground"='SCG';