CREATE TABLE players(
    "player_id" INT PRIMARY KEY,
    "first_name" TEXT,
    "last_name" TEXT,
    "hand" TEXT,
    "birth_date" DATE,
    "country_code" TEXT
)

CREATE TABLE matches(
  "best_of" INT,
  "draw_size" INT,
  "loser_age" FLOAT,
  "loser_entry" TEXT,
  "loser_hand" TEXT,
  "loser_ht" INT,
  "loser_id" INT,
  "loser_ioc" TEXT,
  "loser_name" TEXT,
  "loser_rank" INT,
  "loser_rank_points" INT,
  "loser_seed" INT,
  "match_num" INT,
  "minutes" INT,
  "round" TEXT,
  "score" TEXT,
  "surface" TEXT,
  "tourney_date" DATE,
  "tourney_id" TEXT,
  "tourney_level" TEXT,
  "tourney_name" TEXT,
  "winner_age" FLOAT,
  "winner_entry" TEXT,
  "winner_hand" TEXT,
  "winner_ht" INT,
  "winner_id" INT,
  "winner_ioc" TEXT,
  "winner_name" TEXT,
  "winner_rank" INT,
  "winner_rank_points" INT,
  "winner_seed" INT,
  "year" INT,
  FOREIGN KEY(loser_id) REFERENCES players(player_id),
  FOREIGN KEY(winner_id) REFERENCES players(player_id)
)

CREATE TABLE rankings("ranking_date" DATE,"ranking" INT,"player_id" INT,"ranking_points" INT,"tours" INT,FOREIGN KEY(player_id) REFERENCES players(player_id))
SELECT sum(tours) ,  ranking_date FROM rankings GROUP BY ranking_date
How many total tours were there for each ranking date?