Postgres 13

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE coaches   (id serial PRIMARY KEY, name text);
CREATE TABLE positions (id serial PRIMARY KEY, name text);
CREATE TABLE teams     (id serial PRIMARY KEY, name text);
CREATE TABLE periods   (id serial PRIMARY KEY, team serial REFERENCES teams, year int, wins int, losses int, ties int);
CREATE TABLE periods_positions_coaches_linking (id serial PRIMARY KEY, period int REFERENCES periods, position int REFERENCES positions, coach int REFERENCES coaches);

INSERT INTO coaches (name)   VALUES ('Coach 1');
INSERT INTO teams (name)     VALUES ('StackOverflow Sluggers');
INSERT INTO positions (name) VALUES ('Head Coach'), ('Assistant Coach');

-- 10 games per year/season
INSERT INTO periods (team, year, wins, losses, ties) VALUES
  (1, 2012, 5, 5, 0)   -- 10 in one period
, (1, 2013, 5, 4, 0)   -- two periods, still 10 total
, (1, 2013, 0, 1, 0)
, (1, 2014, 5, 5, 0)   -- 10 in this period but will be double-counted accidentally
;
INSERT INTO periods_positions_coaches_linking (period, position, coach) VALUES
  (1, 1, 1)
, (2, 1, 1)
, (3, 1, 1)
, (4, 1, 1)   -- both assistant and head coach this period
, (4, 2, 1)
;

1 rows affected

1 rows affected

2 rows affected

4 rows affected

5 rows affected

year	position_id	position_names	wins	losses
2012	{1}	{"Head Coach"}	5	5
2013	{1}	{"Head Coach"}	5	5
2014	{1,2}	{"Assistant Coach","Head Coach"}	5	5