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PODo link tables need a meaningless primary key field?
 

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  1. PODo link tables need a meaningless primary key field?
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    <p>I am working on a couple of link tables and I got to thinking (Danger Will Robinson, Danger) what are the possible structures of a link table and what are their pro's and con's.</p> <p>I came up with a few possible strictures for the link table:</p> <h3>Traditional 3 column model</h3> <ul> <li>id - auto-numbered PRIMARY</li> <li>table1fk - foreign key</li> <li>table2fk - foreign key</li> </ul> <p>It's a classic, in most of the books, 'nuff said.</p> <h3>Indexed 3 column model</h3> <ul> <li>id - auto-numbered PRIMARY</li> <li>table1fk - foreign key <code>INDEX ('table1fk')</code></li> <li>table2fk - foreign key <code>INDEX ('table2fk')</code></li> </ul> <p>In my own experience, the fields that you are querying against are not indexed in the traditional model. I have found that indexing the foreign key fields does improve performance as would be expected. Not a major change but a nice optimizing tweak.</p> <h3>Composite key 2 columns <code>ADD PRIMARY KEY ('table1fk' , 'table2fk')</code></h3> <ul> <li>table1fk - foreign key</li> <li>table2fk - foreign key</li> </ul> <p>With this I use a composite key so that a record from table1 can only be linked to a record on table2 once. Because the key is composite I can add records (1,1), (1,2), (2,2) without any duplication errors.</p> <p>Any potential problems with the composite key 2 columns option? Is there an indexing issue that this might cause? A performance hit? Anything that would disqualify this as a possible option?</p>
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    1. USAndrew Medico
    1. USTyson of the Northwest
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      1. VTUpMod
    1. COThis is the same as http://stackoverflow.com/questions/1839584/should-i-use-an-index-column-in-a-many-to-many-link-table
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      1. USRalph Lavelle
    2. COyour right, weird, I didn't find it in the subject search.
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      1. USTyson of the Northwest
 

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