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relational table

hello...
can anyone please help me with that problem,,
i have created two table on Oracle 10g, one called CAR and other called  CUSTOMER,
as the CAR, i have CAR_REG as PK, and as the CUSTOMER i have CUST_NUM as PK. now i want to create a relationship  between them a relational table called HIRE. in HIRE table i want to have CAR_REG as FK, and CUST_NUM as FK, and DATE_HIRED  

i was ok creating the first two main tables for CAR and CUSTOMER, but i am having problem with the commands for the relational table (HIRE) i have used the command to create that, but i had error,
i will be more than thankful with any help,,, thank you
ALTER TABLE CAR
ADD (FOREIGN KEY (CAR_REG) REFERENCES facuty (CUST_NUM));

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ferman-k
Asked:
ferman-k
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1 Solution
 
mrjoltcolaCommented:
Your code snippet has a table named "facuty", what is that? You don't mention it in your question.

Also, it is more common to create the foreign key during the "CREATE TABLE" statement. But since you are trying to add it afterwards, you don't add it to the parent table  (CAR or CUSTOMER), you have to add it to the child table (HIRE). Also, the columns must exist in the child table (car_reg and cust_num)


ALTER TABLE hire
  ADD CONSTRAINT fk_car_reg
     FOREIGN KEY(car_reg)
     REFERENCES car(car_reg)
;
 
ALTER TABLE hire
  ADD CONSTRAINT fk_cust_num
     FOREIGN KEY(cust_num)
     REFERENCES customer(cust_num)
;

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ferman-kAuthor Commented:
I tried your commands exactly the same but it was not recognisable by my system... don't you think it its because that i am using "iSQL* pluse"...?
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mrjoltcolaCommented:
Please post the error messages.
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ferman-kAuthor Commented:
here is the message i get when i try the commands;



 FOREIGN KEY(car_reg)
                 *

ERROR at line 3:
ORA-00904: "CAR_REG": invalid identifier

     FOREIGN KEY(cust_num)
                 *

ERROR at line 3:
ORA-00904: "CUST_NUM": invalid identifier


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mrjoltcolaCommented:
It looks like you don't have columns CAR_REG and CUST_NUM in the appropriate tables. In order to create the foreign key, the column has to exist.

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ferman-kAuthor Commented:
sorry,
yes i have, they both  are pk in their original table
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mrjoltcolaCommented:
Yes, but that is not the foreign key. You need to create identical type columns in the HIRE table before running the commands above.

Can you describe your tables and paste them here?

You did not say what datatypes car_reg and cust_num are. So change them appropriately below or paste them in and I will verify.

Also, it probably makes sense to index these columns, but depends on how you will join them. I would create individual indexes based on the fact that it is a linking table.

create table hire
(
  car_reg varchar2(20) not null, -- change varchar2(20) to actual data type
  cust_num integer not null, -- change integer to actual data type
  date_hired date
);
 
create index ix_hire_car_reg on hire(car_reg);
create index ix_hire_cust_num on hire(cust_num);
 
ALTER TABLE hire
  ADD CONSTRAINT fk_car_reg
     FOREIGN KEY(car_reg)
     REFERENCES car(car_reg)
;
 
ALTER TABLE hire
  ADD CONSTRAINT fk_cust_num
     FOREIGN KEY(cust_num)
     REFERENCES customer(cust_num)
;

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