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    <p>I am assuming that you are dealing with hierarchical data here.</p> <p>You just need two tables. One of the tables is for the categories and relationships between the categories. For example:</p> <pre><code>CategoryID CategoryName ParentCategoryID ---------------------------------------- 1 Computers NULL 2 Programming 1 3 Games 1 4 Python 2 </code></pre> <p>The other table is for storing the data associated with the categories. For example:</p> <pre><code>CategoryID ItemID Description ---------------------------------------------- 4 1 Book – Programming in Python 3 1 World of Warcraft </code></pre> <p>The first table contains a foreign key column that links the subcategories to their parent categories. This is known as the “Adjacency List Model”. This model has the advantage of being simple to understand and doing various things (e.g. retrieving the path to the Python category – /Computers/Programming/Python) with this model can be done quite easily with client-side code (if you don’t mind the performance cost because you may need to make multiple queries to the database). However, it can be mindboggling if you try to do it in full SQL. For example, retrieving the path for a category will require self-joins.</p> <p>Another way of structuring this table is to think of the categories and sub-categories as sets and subsets (known as the “Nested Set Model”). It’s hard to explain this model without diagrams, and the article <a href="http://mikehillyer.com/articles/managing-hierarchical-data-in-mysql/" rel="nofollow noreferrer">Managing Hierarchical Data in MySQL</a> seems to do a better job in explaining the concepts (both “Adjacency List” and “Nested Set” models).</p>
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    1. POWhat would be the best way to design database and relationships for a website like Yelp or eBay (lots of categories and sub-categories)?
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    1. USPaŭlo Ebermann
    1. USmaxyfc
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    1. POWhat would be the best way to design database and relationships for a website like Yelp or eBay (lots of categories and sub-categories)?
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    1. COYour solution looks like the most scalable with the least amount of work (no need to keep creating tables). The Nested Set model is absolutely gorgeous, and I found a Rails plugin that I assume makes it easier to work with them. Thanks!
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      1. USSan Diago
    2. COThanks maxyfc. This really helped me.
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      1. USYogi Yang 007
 

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