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SQL PrimaryKey best practice

Posted on 2011-03-16
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?
Question by:AkAlan
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LVL 29

Assisted Solution

by:Paul Jackson
Paul Jackson earned 333 total points
ID: 35149761
Yes that's the only way to meet all your conditions.

Author Comment

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

Assisted Solution

by:Paul Jackson
Paul Jackson earned 333 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
LVL 10

Accepted Solution

Asim Nazir earned 167 total points
ID: 35149831
You can also Add Unique constraint to two of the fields i.e. other than one PK field.

Author Closing Comment

ID: 35162240
Thanks to both.

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