Comments on: How do I use primary keys in SQL server? http://itknowledgeexchange.techtarget.com/itanswers/sql-server-11/ Wed, 22 May 2013 05:05:11 +0000 hourly 1 By: The Most-Watched IT Questions: September 21, 2010 - ITKE Community Blog http://itknowledgeexchange.techtarget.com/itanswers/sql-server-11/#comment-81691 The Most-Watched IT Questions: September 21, 2010 - ITKE Community Blog Tue, 21 Sep 2010 06:37:49 +0000 #comment-81691 [...] 10. Shamu got some in-depth feedback from Mr. Denny, Kccrosser and TomLiotta: How do I use primary keys in SQL Server? [...]

]]> By: tomliotta http://itknowledgeexchange.techtarget.com/itanswers/sql-server-11/#comment-81313 tomliotta Thu, 09 Sep 2010 00:45:13 +0000 #comment-81313 It’s reasonable that a given SUBJECT might relate to more than one COURSE. A TEACHER might relate to a single SUBJECT; and through the relationship to SUBJECT, multiple COURSEs might be reached.

However, there is no way to know what keys might be needed as either primary keys or foreign until the rules of relationships are established.

How many SUBJECTs can a TEACHER teach? Only one? More than one?
Is every TEACHER required to have a related SUBJECT?
Can a SUBJECT be taught by more than one TEACHER?
How many COURSEs can a SUBJECT have?
Can a COURSE be part of more than one SUBJECT?
Are TEACHERs related to SUBJECTs or to COURSEs?

The structure should be set up to match reality as far as possible. One aspect of reality is that it can change with very little notice ahead of time. That means that some flexibility might be useful.

Today, each TEACHER might teach only a single COURSE. Tomorrow, a TEACHER might need to teach every COURSE within a SUBJECT. Next week, a TEACHER might need to teach multiple SUBJECT.

Start by determining what actually happens today. Then start questioning today’s rules to see how unbreakable they are.

Tom

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