How to have multiple rows reference the same field of a single row?

I'm new to PostgreSQL and forming relationships between tables. I have a jobs table and an items table. The jobs table has a shipping_date. I would like the items table to have a column that reflects the shipping_date of the jobs table:

jobs table:

job_id | shipping_date
10001  | 29-06-2014
10002  | 29-06-2014
10003  | 30-06-2014


items table:

item_id | job_id      | shipping_date
1234    | fkey(10001) | need this to be 29-06-2014 
1235    | 10001       | need this to be 29-06-2014

Shipping date can't be a fkey as it is not unique but we need it to reference the relevant shipping_date from jobs table.

Each job can have several associated items. Each item can only be associated with one job.

Thank you!

Solution

You don't want to have redundancy in your database. You could create a view that joins the two tables and show you what you need. The select could be:

SELECT a.item_id, a.job_id, b.shipping_date
  FROM items a INNER JOIN jobs b ON a.job_id = b.job_id