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SQL PrimaryKey best practice

Posted on 2011-03-16
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Last Modified: 2012-05-11
I am creating a table ProjectSites that will be a child table to another table Projects and it will only have three columns, here is the current schema

ProjectSites Table:

ProjectSiteID          identity  pk
ProjectID                int          fk
SiteID                     int          fk

So the idea is, there can be one or more Sites assigned to every project. There will never be a case where the same Site is assigned more than once to the same Project. My question is this, Should I make the PK of the table a combination of all three columns so that no mistakes can ever be made?
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Question by:AkAlan
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5 Comments
 
LVL 29

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by:Paul Jackson
Paul Jackson earned 1332 total points
ID: 35149761
Yes that's the only way to meet all your conditions.
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LVL 6

Author Comment

by:AkAlan
ID: 35149770
Ok, I thought that was so, I was just thinking about any performance issues that could cause. Thanks.
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LVL 29

Assisted Solution

by:Paul Jackson
Paul Jackson earned 1332 total points
ID: 35149796
Will it impact performance? yes but  marginally given they are int columns. It is unavoidable given the requirements specified and best practice
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LVL 10

Accepted Solution

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Asim Nazir earned 668 total points
ID: 35149831
You can also Add Unique constraint to two of the fields i.e. other than one PK field.
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LVL 6

Author Closing Comment

by:AkAlan
ID: 35162240
Thanks to both.
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