Question

All –
I need some help designing a table for a Postgre SQL database. I have a table of products ie;

CREATE TABLE products (  
    product_id integer PRIMARY KEY,  
    product_name text,  
    price numeric);  

INSERT INTO products (product_id, product_name, price) VALUES   
(DEFAULT, 'Purple Widget', '5.50'),  
(DEFAULT, 'Green Widget', '1.50'),  
(DEFAULT, 'Yellow Widget', '5.50'),  
(DEFAULT, 'Spotted Widget', '6.50'),  
(DEFAULT, 'Extra Large Purple Widget', '102.50'),  
(DEFAULT, 'Extra Large Spotted Widget', '101.50');    

I want to start selling a package of products (multiple products, one price). I am trying to figure out a structure for a packages table. Two options I don’t like are –

CREATE TABLE packages (  
    package_id integer PRIMARY KEY,   
    package_name text,
    package_products varchar(50),  
    price numeric);  

INSERT INTO packages (package_id, package_name, package_products, price) VALUES  
    (DEFAULT, 'Small Widgets', '0,1,2,3', '6.25'),  
    (DEFAULT, 'Large Widgets', '5,6', '200.00');  

or

CREATE TABLE packages (  
    package_id integer PRIMARY KEY,   
    package_name text,
    product_id1 integer,  
    product_id2 integer,  
    product_id3 integer,  
    product_id4 integer,  
    product_id5 integer,  
    price numeric);  

INSERT INTO packages (package_id, package_name, product_id1, product_id2, 
                      product_id3, product_id4, product_id5, price) VALUES  
    (DEFAULT, 'Small Widgets', '0', '1' ,'2', '3', NULL, '6.25'),  
    (DEFAULT, 'Large Widgets', '5', '6', NULL, NULL, NULL, '200.00');  

I can’t move the packages logic to the products table because each product could be in multiple packages. Both of those options above require a lot of work at the web layer to make work, plus they both seem really inefficient.

Ideas? Thanks in advance!

Answer 1

This is a standard many-to-many relationship (many packages to many items)

CREATE TABLE products (
product_id integer PRIMARY KEY,
product_name text,
price numeric);

CREATE TABLE packages (
package_id integer PRIMARY KEY,
package_name text,
price numeric); 

CREATE TABLE package_items (
package_item_id integer PRIMARY KEY,
package_id integer,
product_id integer,
qty integer );