Oracle SQL constraint, name entered must be a member - sql

Question

I have created a tennis club database. This database contains the following tables:
The player table
CREATE TABLE player
(
member_id INT PRIMARY KEY NOT NULL,
member_name VARCHAR2(70) NOT NULL,
date_of_birth DATE,
member_address VARCHAR2(300),
contact_number INT NOT NULL,
gender VARCHAR2(1) NOT NULL CHECK(gender IN('f','m')),
club_seeding INT NOT NULL,
county_seeding INT NOT NULL,
renewal_date DATE,
m_type VARCHAR(9) NOT NULL CHECK(m_type IN('junior','student', 'senior', 'family', 'associate'))
);
This consists of members of the tennis club.
And then there is the team table
CREATE TABLE team
(
team_id INT PRIMARY KEY NOT NULL,
club_seeding INT,
county_seeding INT,
player1 VARCHAR2(70) NOT NULL,
player2 VARCHAR2(70) NOT NULL,
team_name VARCHAR2(145) NOT NULL
);
This is used to enter 2 players to form a doubles team.
My question is how could I create a constraint that only allows players(member_name) from the player table to be entered into the team table?

Answer 1

you need create foreign key constraints
see docs here
but in your sample you need change type of player1 and player2 columns from varchar to int:
sample of alter table statements
-- Create foreign key constraints
alter table TEAM
add constraint fk_team_player_1 foreign key (PLAYER1)
references player (MEMBER_ID);
alter table TEAM
add constraint fk_team_player_2 foreign key (PLAYER2)
references player (MEMBER_ID);
sample of createing FK contstraints in table
CREATE TABLE team
(
team_id INT PRIMARY KEY NOT NULL,
club_seeding INT,
county_seeding INT,
player1 INT NOT NULL,
player2 INT NOT NULL,
team_name VARCHAR2(145) NOT NULL
,constraint fk_team_player_1 foreign key (PLAYER1)
references player (MEMBER_ID)
,constraint fk_team_player_2 foreign key (PLAYER2)
references player (MEMBER_ID)
);
if you want to use member names as PK
CREATE TABLE player
(
member_name VARCHAR2(70) PRIMARY KEY NOT NULL,
date_of_birth DATE,
member_address VARCHAR2(300),
contact_number INT NOT NULL,
gender VARCHAR2(1) NOT NULL CHECK(gender IN('f','m')),
club_seeding INT NOT NULL,
county_seeding INT NOT NULL,
renewal_date DATE,
m_type VARCHAR(9) NOT NULL CHECK(m_type IN('junior','student', 'senior', 'family', 'associate'))
);
CREATE TABLE team
(
team_id INT PRIMARY KEY NOT NULL,
club_seeding INT,
county_seeding INT,
player1 VARCHAR2(70) NOT NULL,
player2 VARCHAR2(70) NOT NULL,
team_name VARCHAR2(145) NOT NULL
,constraint fk_team_player_1 foreign key (PLAYER1)
references player (member_name)
,constraint fk_team_player_2 foreign key (PLAYER2)
references player (member_name)
);