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Bad Microsoft DB Schema Example
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Bad Microsoft DB Schema Example
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okkko
okkko
Posted Thursday, June 12, 2008 8:15 AM
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OK, generally I try to avoid or ignore bad things. But I think this is important. I'm relearning about DB design concepts and I stumbled upon this Microsoft examples page. I haven't looked closely to all of them but the one example that even has a video is
3rd example
.
And here's the image:
What really bothers me is that they have a "real-world" examples and then they create a table Products that holds the data for both books and coffee!
So, even if there is a store that sells books and coffee (I guess it's possible), wouldn't it be better if there was a general "Products" table and then two separate tables for "Books" and "Coffee" with specific columns?
Somebody enlighten me please why they put such example on their official page and tell me if I'm right. What if the store sold just 10 different product and each product has only 10 specific columns - a table with 100+ columns! I am 98% sure this is really bad table design and should be avoided.
p.s.: A link with better real-world examples possible with tables?
Post #515955
Christopher Stobbs
Christopher Stobbs
Posted Thursday, June 12, 2008 8:18 AM
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Other thing is to maybe create a ProductsBook and ProductsFood table?
What do people think of this?
----------------------------------------------
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- Thomas Henry Huxley
Posting Best Practices
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SQL-4-Life
Post #515959
Lynn Pettis
Lynn Pettis
Posted Thursday, June 12, 2008 8:31 AM
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Not knowing the full details of the example it is difficult to make a judgement. One thing to remember is that while designing a database for a production application (as opposed to one for database class) you will make decisions to denormalize a design for performance reasons. Although it may make sense to split off those aspects of the data that relate only to books or coffee into their own table, you may experience performance issues as you increase the number of tables you have to join in a query.
Lynn Pettis
For better assistance in answering your questions, click here
For tips to get better help with Performance Problems, click here
For Running Totals and its variations, click here
or
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For more about Tally Tables, click here
For more about Cross Tabs and Pivots, click here
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Post #515968
okkko
okkko
Posted Thursday, June 12, 2008 8:45 AM
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Lynn Pettis (6/12/2008)
Not knowing the full details of the example it is difficult to make a judgement. One thing to remember is that while designing a database for a production application (as opposed to one for database class) you will make decisions to denormalize a design for performance reasons. Although it may make sense to split off those aspects of the data that relate only to books or coffee into their own table, you may experience performance issues as you increase the number of tables you have to join in a query.
As in? Like when you'd want to see all data of all products that were ordered on a certain date? If it's just one Products table this is fast as opposed to each product in a separate table? Wouldn't that query look a mess and all columns irrelevant to a product (book_author for coffee) would be null?
What if you have 50 products?
Post #515985
Christopher Stobbs
Christopher Stobbs
Posted Thursday, June 12, 2008 8:48 AM
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WEll you need to remember that you shouldn't use SELECT * so you should return the book columns in a food query
----------------------------------------------
Try to learn something about everything and everything about something.
- Thomas Henry Huxley
Posting Best Practices
Numbers / Tally Tables
SQL-4-Life
Post #515989
okkko
okkko
Posted Thursday, June 12, 2008 8:53 AM
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Christopher Stobbs (6/12/2008)
WEll you need to remember that you shouldn't use SELECT * so you should return the book columns in a food query
Hehe, yes of course. :D How would you return just the relevant product data for each product?
Anyway, so this example diagram is not so bad after all? And just because of the performance issues?
Post #515997
Lynn Pettis
Lynn Pettis
Posted Thursday, June 12, 2008 10:01 AM
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I'm not making any judgements on the design. I was trying to point out that somethings that don't seem right could be based on other factors.
You could desgin a database system that totally eliminates all null values in tables. It has a name, 6th normal form. Would I implement such a design for an OLTP system, no. Biggest reason, performance. The number of table joins required to pull data together would be costly.
Also, in this design, you are only looking at the database schema. I have no idea what the UI design is. It may take into account the different products and use different screens or web pages dependent on the product type. From what was posted, that is unknown.
Also, you should never use a SELECT * FROM ... in your production code.
Lynn Pettis
For better assistance in answering your questions, click here
For tips to get better help with Performance Problems, click here
For Running Totals and its variations, click here
or
when working with partitioned tables
For more about Tally Tables, click here
For more about Cross Tabs and Pivots, click here
and
here
Managing Transaction Logs
SQL Musings from the Desert
Fountain Valley SQL
(My Mirror Blog)
Post #516066
Grant Fritchey
Grant Fritchey
Posted Thursday, June 12, 2008 11:18 AM
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Unless there's a pretty major application or performance reason, I'd have to agree that this is a crappy "real world" example.
----------------------------------------------------
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Post #516113
Matt Miller (#4)
Matt Miller (#4)
Posted Thursday, June 12, 2008 11:31 AM
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Grant Fritchey (6/12/2008)
Unless there's a pretty major application or performance reason, I'd have to agree that this is a crappy "real world" example.
Not fully understanding the background on how that was used - was it being portrayed as being a crappy model example or was this the final result? Because that's a fairly ugly example to be sure.
----------------------------------------------------------------------------------
Your lack of planning does not constitute an emergency on my part...unless you're my manager...or a director and above...or a really loud-spoken end-user..All right - what was my emergency again?
Post #516123
okkko
okkko
Posted Thursday, June 12, 2008 11:38 AM
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Group: General Forum Members
Last Login: Saturday, August 28, 2010 1:06 AM
Points: 19,
Visits: 82
It seems that some of you have missed my link:
source page
Post #516135
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