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POWhy does my database table need a primary key?
 

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  1. POWhy does my database table need a primary key?
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    <p>In my database I have a list of users with information about them, and I also have a feature which allows a user to add other users to a shortlist. My user information is stored in one table with a primary key of the user id, and I have another table for the shortlist. The shortlist table is designed so that it has two columns and is basically just a list of pairs of names. So to find the shortlist for a particular user you retrieve all names from the second column where the id in the first column is a particular value.</p> <p>The issue is that according to many sources such as this <a href="https://stackoverflow.com/questions/840162/should-each-and-every-table-have-a-primary-key">Should each and every table have a primary key?</a> you should have a primary key in every table of the database.</p> <p>According to this source <a href="http://www.w3schools.com/sql/sql_primarykey.asp" rel="nofollow noreferrer">http://www.w3schools.com/sql/sql_primarykey.asp</a> - a primary key in one which uniquely identifies an entry in a database. So my question is:</p> <ol> <li><p>What is wrong with the table in my database? Why does it need a primary key?</p></li> <li><p>How should I give it a primary key? Just create a new auto-incrementing column so that each entry has a unique id? There doesn't seem much point for this. Or would I somehow encapsulate the multiple entries that represent a shortlist into another entity in another table and link that in? I'm really confused.</p></li> </ol>
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    1. USuser1058210
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    1. COTry it with just an index, you don't need a primary key. Get numbers as to performance without one, see if it is fast enough.
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      1. POWhy does my database table need a primary key?
      1. USJames Black
    2. COThanks I'll try that. From a proper relational point of view though, how would you go about doing something like this? It's not like you can create another table to represent a shortlist for a single person because that would also need to accomodate the fact that we don't know how many people the person will add to it. So you can't have a separate column for each - you need a new row - back to the same situation haha!
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      1. POWhy does my database table need a primary key?
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    3. COYou create a table that has two user ids as the columns, so you can relate a person to someone else, and if you want to enforce uniqueness then create a primary key that is composed of both columns.
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      1. USJames Black
 

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