外键- SQL 开发人员

Question

So the problem im having is the foreign keys in my table, when I run without the foreign key is creates the tables. the error im will be posted at the bottom, Just trying to get familiar with SQL.

CREATE TABLE Player
(
Player_ID VARCHAR(20) NOT NULL,
Fname VARCHAR(15),
Sname VARCHAR(15),
DOB    NUMBER(3),
Height NUMBER(3),
Weight NUMBER(3),
Position VARCHAR(15),
Team_ID VARCHAR(20) NOT NULL,

CONSTRAINT Player_primary_key PRIMARY KEY (Player_ID),
CONSTRAINT Player_foreign_key FOREIGN KEY(Team_ID) REFERENCES TEAM(Team_ID)
);


CREATE TABLE Team
(
Team_ID VARCHAR(20) NOT NULL,
Tname VARCHAR(20),
Tlocation VARCHAR(20),
Coach VARCHAR(20),
Gameswon NUMBER(10),
Gameslost NUMBER (10),

CONSTRAINT Team_primary_key PRIMARY KEY (Team_ID)
);


CREATE TABLE Match
(
Match_ID VARCHAR(20) NOT NULL,
Hometeam VARCHAR(20), 
Awayteam VARCHAR(20), 
Score NUMBER (10),
Mdate NUMBER(10),
Mtime NUMBER(10),

CONSTRAINT Match_primary_key PRIMARY KEY (Match_ID),
CONSTRAINT Match_foreign_keyHome FOREIGN KEY (Team_ID) REFERENCES HOST(Team_ID),
CONSTRAINT Match_foreign_keyAway FOREIGN KEY (Team_ID) REFERENCES TEAM(Team_ID)
);

CREATE TABLE HOST
(
Team_ID VARCHAR(20) NOT NULL,
Match_ID VARCHAR(20) NOT NULL,

CONSTRAINT Host_Foriegn_Key_Team FOREIGN KEY (Team_ID) REFERENCES TEAM(Team_ID),
CONSTRAINT Host_Foriegn_Key_Match FOREIGN KEY (Match_ID) REFERENCES MATCH(Match_ID)
);

Answer 1

Well your first error seems to be related to the fact that you have not defined the Team table yet. Since you are using:

CONSTRAINT Player_foreign_key FOREIGN KEY(Team_ID) REFERENCES TEAM(Team_ID)

For the Match table you are creating a foreign key with Team_ID even though it does not exist in your table. That's why it's throwing the error:

CONSTRAINT Match_foreign_keyAway FOREIGN KEY (Team_ID) REFERENCES TEAM(Team_ID)

And for your last error MATCH is actually a SQL command which is why it turns blue when you put it as a code sample. I'm thinking this is why it's looking for a table name but assuming you're not providing one. That's just my guess for the last error.

1) So I would first create your Team table instead of creating Player first.
2) Then I would probably change Team_ID for Match_foreign_keyHome to Hometeam:

CONSTRAINT Match_foreign_keyHome FOREIGN KEY (Hometeam) REFERENCES HOST(Team_ID),

And then I would change Team_ID for Match_foreign_keyAway to Awayteam:

CONSTRAINT Match_foreign_keyHome FOREIGN KEY (Awayteam) REFERENCES HOST(Team_ID),