SQL ALTER TABLE foreign key - sql

Question

I have a problem with adding foreign keys with alter table command. I don't know how to make it so it works.
I need to add ISIK_ID and STAADION_ID to ISIK_STAADIONIL table as foreign key.
Here is my code:
CREATE TABLE ISIK(
ISIK_ID INT NOT NULL,
EESNIMI VARCHAR(25) NOT NULL,
PEREKONNANIMI VARCHAR(25) NOT NULL,
ISIKUKOOD VARCHAR(20),
KODAKONDSUS VARCHAR(30),
SUGU CHAR(1) NOT NULL,
HARIDUSTASE CHAR(1) NOT NULL,
TELEFONI_NR VARCHAR(20),
SYNNIPAEV DATE,
CONSTRAINT ISIK_ID_PK PRIMARY KEY (ISIK_ID)
);
CREATE TABLE ISIK_STAADIONIL(
ISIK_STAADIONIL_ID INT NOT NULL,
CONSTRAINT ISIK__STAADIONIL_ID_PK PRIMARY KEY (ISIK_STAADIONIL_ID),
ALATES TIMESTAMP,
KUNI TIMESTAMP
);
CREATE TABLE STAADION(
STAADION_ID INT NOT NULL,
NIMETUS VARCHAR(20),
KIRJELDUS VARCHAR(100),
ASUKOHT VARCHAR(50),
SUURUS VARCHAR(20),
MAHUTAVUS INT,
EHITATUD VARCHAR(20),
EHITAJA VARCHAR(20),
CONSTRAINT STAADION_ID_PK PRIMARY KEY (STAADION_ID)
);
ALTER TABLE ISIK_STAADIONIL
ADD CONSTRAINT ISIK_ID_FK
FOREIGN KEY(ISIK_ID)
REFERENCES ISIK(ID);

Answer 1

You need to add the columns first (to the table) before you can create FK constraints using them.
CREATE TABLE ISIK_STAADIONIL(
ISIK_STAADIONIL_ID INT NOT NULL,
CONSTRAINT ISIK__STAADIONIL_ID_PK PRIMARY KEY (ISIK_STAADIONIL_ID),
ALATES TIMESTAMP,
KUNI TIMESTAMP,
ISIK_ID INT,
STAADION_ID INT
);
And then your ALTER statement should work fine.
UPDATE
Changing the table-design slightly would make more sense, as per following. The logic is that ISIK_ID and STAADION_ID would together be sufficient to determine uniqueness in the ISIK_STAADIONIL table, so a separate ID is redundant:
CREATE TABLE ISIK_STAADIONIL(
ISIK_ID INT NOT NULL,
STAADION_ID INT NOT NULL,
CONSTRAINT ISIK__STAADIONIL_ID_PK PRIMARY KEY (ISIK_ID, STAADION_ID),
ALATES TIMESTAMP,
KUNI TIMESTAMP
);