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Allen White

T-SQL Tuesday #3: Database Relationships

In my first T-SQL Tuesday submission I thought I'd mention something that we often take for granted when working with relational databases.

At the basic level, a database table is really a relation. You can have a truly relational database with just a single table. The relationship is that between each of the attributes (or columns) with the candidate key (usually the primary key). Each attribute is dependent, in a properly normalized database, on that key, and so a single table database is still a relational database.

In the data structures I've seen over the years I've seen too many examples where multiple dependencies within a row cause problems, so it's good to revisit the basics now and then.

Enjoy the rest of your day!


Published Tuesday, February 9, 2010 10:29 PM by AllenMWhite



Cade Roux said:


It's a pet peeve of mine that some people continue to say relational databases are called that because different tables can be joined together.  I guess it's a small consolation that people have forgotten where things came from and that RDBMS have become ubiquitous and we no longer have nearly as many crazy file and hierarchical database which follow all kinds of relatively insane rules.

Data modelling is hard in general, but it is certainly a lot easier when people don't handicap themselves by forgetting the ideas about "key, the whole key and nothing but the key" rules and the idea that a table is the definition of a relation (to a key).

February 10, 2010 10:36 AM

David said:

Doesn't it say something about the state of the IT industry that many database professionals don't even know what relational means?

February 11, 2010 1:37 PM

Rob Farley said:

(Reposted from my blog ) Lots of blog posts for this month, for the first T-SQL Tuesday to

February 20, 2010 1:32 AM

ascdgvfg said:


December 12, 2011 1:30 AM
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About AllenMWhite

Allen White is a consultant and mentor for Upsearch Technology Services in Northeast Ohio. He has worked as a Database Administrator, Architect and Developer for over 30 years, supporting both the Sybase and Microsoft SQL Server platforms over that period.

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