SQL CROSS JOINs

CREATE SEQUENCE IF NOT EXISTS fixtures_id_seq;

CREATE TABLE "public"."fixtures" (
  "id" int4 NOT NULL DEFAULT nextval('fixtures_id_seq'::regclass),
  "start_time" TIMESTAMPTZ,
  "sport" VARCHAR(40),
  PRIMARY KEY ("id")
);

WITH sports AS (
  SELECT
    DISTINCT sport
  FROM
    fixtures
  ORDER BY
    sport
),
days AS (
  SELECT
    day
  FROM
    generate_series(
      date_trunc('day', '2020-09-09'::date)::date,
      date_trunc('day', '2020-09-21'::date)::date,
      '1 day'::interval
    ) AS day
),
fixtures_per_day AS (
  SELECT
    date_trunc('day', start_time) AS day,
    sport,
    COUNT(*) AS c
  FROM
    fixtures
  GROUP BY
    date_trunc('day', start_time),
    sport
)
SELECT
  days.day,
  sports.sport,
  COALESCE(fixtures_per_day.c, 0) AS fixture_count
FROM
  days
  CROSS JOIN sports
  INNER JOIN fixtures_per_day ON (
    days.day = fixtures_per_day.day
    AND sports.sport = fixtures_per_day.sport
  )

result = []

for day in days:
    for sport in sports:
        result.append((day, sport))