“Cannot add foregin key constraint”

Question

 DROP TABLE IF EXISTS CARD_ACCOUNT; Create Table CARD_ACCOUNT( acct_no Char(16), exp_date date, card_type ENUM('Debit','Credit') NOT NULL, cust_ID integer NOT NULL ); DROP TABLE IF EXISTS DEBIT_CARD; Create Table DEBIT_CARD( acct_no Char(16), exp_date date, bank_no CHAR(9) NOT NULL, Constraint debit_card_pk primary key(acct_no,exp_date), Constraint debit_card_fk foreign key(acct_no,exp_date) References card_account(Acct_no,exp_date) ON UPDATE CASCADE ON DELETE CASCADE ); 

When I try to run this statement I get a "Cannot add foregin key constraint" error in Mysql on the Debit_Card table, why do I get this error the script I am learning from has everything writen the same exact way as I have.

Answer 1

card_account(Acct_no,exp_date) must be Primary Key if you want reference to it in Foreign Key.

and why you don't make it into 1 table?

Create Table CARD_ACCOUNT(
   acct_no Char(16),
   exp_date date,
   bank_no CHAR(9) NOT NULL,
   card_type ENUM('Debit','Credit') NOT NULL,
   cust_ID integer NOT NULL,
   Constraint CARD_ACCOUNT_PK primary key(acct_no,exp_date)
);

i think it serve the same purpose. you already have card_type to know if its debit or credit card so why make separate table for that?

Answer 2

Use the below code, I have just added one primary key constraint in the first table, it will allow you to create the foreign key. But, as " Tim Biegeleisen " commented there is database design problem, you should think again about your database design.

DROP TABLE IF EXISTS CARD_ACCOUNT;
Create Table CARD_ACCOUNT(
acct_no Char(16),
exp_date date,
card_type ENUM('Debit','Credit') NOT NULL,
cust_ID integer NOT NULL,
Constraint debit_card_pk primary key(acct_no,exp_date)
);

DROP TABLE IF EXISTS DEBIT_CARD;
Create Table DEBIT_CARD(
acct_no Char(16),
exp_date date,
bank_no CHAR(9) NOT NULL,
Constraint debit_card_pk primary key(acct_no,exp_date),
Constraint debit_card_fk foreign key(acct_no,exp_date) References card_account(Acct_no,exp_date)
ON UPDATE CASCADE
ON DELETE CASCADE
);