FAQ: What Are Database Relationships? - One-to-One Relationship

This community-built FAQ covers the “One-to-One Relationship” exercise from the lesson “What Are Database Relationships?”.

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This exercise can be found in the following Codecademy content:

Design Databases With PostgreSQL

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I’m getting an error in the last step of this exercise and I can’t figure out why. The previous step had me copy and paste all the “INSERT” statements into this code and it originally included one more insert statement that I have since removed that was meant to purposely throw an error. Any help is appreciated.

‘isbn’ is the primary key for the ‘book’ table, and ‘book_isbn’ is the foreign key that relates to it from the ‘book_details’ table.

  id integer PRIMARY KEY,
  book_isbn varchar(50) REFERENCES book(isbn) UNIQUE,
  rating decimal,
  language varchar(10),
  keywords text[],
  date_published date
);

SELECT
  constraint_name, table_name, column_name
FROM
  information_schema.key_column_usage
WHERE
  table_name = 'book_details';

SELECT
  constraint_name, table_name, column_name
FROM
  information_schema.key_column_usage
WHERE
  table_name = 'book';

INSERT INTO book VALUES (
  'Learn PostgreSQL',
  '123457890',
  100,
  2.99,
  'Great course',
  'Codecademy'
);

INSERT INTO book_details VALUES (
  1,
  '123457890',
  3.95,
  'English',
  '{sql, postgresql, database}',
  '2020-05-20'
);

SELECT
  book.title,
  book.price,
  book_details.language,
  book_details.rating
FROM
  book, book_details
WHERE
  book.isbn = book_details.book_isbn;

I just now realized there is a “Show Solution” button. lol
It appears that the problem came from me deleting the aforementioned code, and also from me adding the code to check the primary key of the ‘book’ table.

1 Like

Solution for last step using the method not given in the solution:

select book.title, book.price, book_details.language, book_details.rating
from book, book_details
where book.isbn = book_details.book_isbn