I have been trying to make my first ever database in SQL. I have a couple of questions for the code I posted at the end of this post.
Are some of the foreign keys redundant?
What would be a decent join on 4 tables?
What would be a good outer-join?

Any help will do

Regards,
Rowan


Code:
CREATE TABLE CLUB(
cl_id		INT		PRIMARY KEY		NOT NULL,
naam		TEXT					NOT NULL,
adres		VARCHAR(200)				NOT NULL,
dtm_opricht	TEXT					NOT NULL
);


CREATE TABLE STADION(
sta_id		INT		PRIMARY KEY		NOT NULL,
cl_id		INT		REFERENCES CLUB(cl_id),
naam		TEXT 					NOT NULL,
adres		VARCHAR(200)				NOT NULL,
capaciteit	INT					NOT NULL,
dtm_bouw	TEXT					NOT NULL
);

CREATE TABLE TECHNISCHDIRECTEUR(
td_id		INT		PRIMARY KEY		NOT NULL,
cl_id		INT		REFERENCES CLUB(cl_id),
naam		TEXT 					NOT NULL,
adres		VARCHAR(200)				NOT NULL,
salaris		REAL					NOT NULL,
nationaliteit 	TEXT					NOT NULL,
geslacht	CHAR					NOT NULL,
dtm_geboorte    TEXT					NOT NULL
);

CREATE TABLE FINANCIEELDIRECTEUR(
fd_id		INT		PRIMARY KEY		NOT NULL,
cl_id		INT		REFERENCES CLUB(cl_id),
naam		TEXT 					NOT NULL,
adres		VARCHAR(200)				NOT NULL,
salaris		REAL					NOT NULL,
nationaliteit 	TEXT					NOT NULL,
geslacht	CHAR					NOT NULL,
dtm_geboorte    TEXT					NOT NULL
);


CREATE TABLE HOOFDTRAINER(
ht_id		INT		PRIMARY KEY		NOT NULL,
cl_id		INT		REFERENCES CLUB(cl_id),
td_id		INT		REFERENCES TECHNISCHDIRECTEUR(td_id),
naam		TEXT 					NOT NULL,
adres		VARCHAR(200)				NOT NULL,
salaris		REAL					NOT NULL,
nationaliteit 	TEXT					NOT NULL,
geslacht	CHAR					NOT NULL,
dtm_geboorte    TEXT					NOT NULL
);


CREATE TABLE ASSISTENTTRAINER(
at_id		INT		PRIMARY KEY		NOT NULL,
cl_id		INT		REFERENCES CLUB(cl_id),
ht_id		INT		REFERENCES HOOFDTRAINER(ht_id),
naam		TEXT 					NOT NULL,
adres		VARCHAR(200)				NOT NULL,
salaris		REAL					NOT NULL,
nationaliteit 	TEXT					NOT NULL,
geslacht	CHAR					NOT NULL,
dtm_geboorte    TEXT					NOT NULL
);

CREATE TABLE SPELER(
sp_id		INT		PRIMARY KEY		NOT NULL,
cl_id		INT		REFERENCES CLUB(cl_id),
ht_id		INT		REFERENCES HOOFDTRAINER(ht_id),
naam		TEXT 					NOT NULL,
adres		VARCHAR(200)				NOT NULL,
salaris		REAL					NOT NULL,
nationaliteit 	TEXT					NOT NULL,
geslacht	CHAR					NOT NULL,
dtm_geboorte    TEXT					NOT NULL,
positie		TEXT					NOT NULL,
rugnummer	INT					NOT NULL
);