SQL Clone
SQLServerCentral is supported by Redgate
 
Log in  ::  Register  ::  Not logged in
 
 
 


Maximum number of dimensions and facts in Star schema?


Maximum number of dimensions and facts in Star schema?

Author
Message
mkkrishna
mkkrishna
Forum Newbie
Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)

Group: General Forum Members
Points: 2 Visits: 0
What is maximum number of dimensions tables in Star schema?
And within the fact table, what is the maximum number of facts?
Koen Verbeeck
Koen Verbeeck
One Orange Chip
One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)

Group: General Forum Members
Points: 28037 Visits: 13268
I don't think there is a hard-coded limit.
But if your number of dimensions is going over 30, you might want to investigate of some dimensions can't be combined.

Regarding facts: if they are calculated facts based upon other facts in the same table, leave them out. The reporting layer can do that as well.
If all the facts are valid measurements of your business process, you don't have too many facts.


How to post forum questions.
Need an answer? No, you need a question.
What’s the deal with Excel & SSIS?
My blog at SQLKover.

MCSE Business Intelligence - Microsoft Data Platform MVP
mkkrishna
mkkrishna
Forum Newbie
Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)Forum Newbie (2 reputation)

Group: General Forum Members
Points: 2 Visits: 0
Hi,

Can I know in terms of relation between fact table and dimension table.
Could one fact table be connected to a maximum of 16 dimension tables?

Regards
Koen Verbeeck
Koen Verbeeck
One Orange Chip
One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)One Orange Chip (28K reputation)

Group: General Forum Members
Points: 28037 Visits: 13268
You can connect a fact table to as many dimension tables as you like. There's no technical limit on that.
You just have to make sure that it make sense to link a fact table to a certain dimension.

There are practical limits though. Having too much dimensions makes it unwieldy to browse through the cube (especially in Excel).
Personally I try to stay below 15 dimensions, ideally below 10.


How to post forum questions.
Need an answer? No, you need a question.
What’s the deal with Excel & SSIS?
My blog at SQLKover.

MCSE Business Intelligence - Microsoft Data Platform MVP
sneumersky
sneumersky
SSCrazy
SSCrazy (2.5K reputation)SSCrazy (2.5K reputation)SSCrazy (2.5K reputation)SSCrazy (2.5K reputation)SSCrazy (2.5K reputation)SSCrazy (2.5K reputation)SSCrazy (2.5K reputation)SSCrazy (2.5K reputation)

Group: General Forum Members
Points: 2510 Visits: 487
I agree with Koen. The KimballGroup states that 5 to 15 dimensions is usually the most common range and that is at the PHYSICAL LEVEL. The only thing I would add is that 3 role playing dimensions based off the same PHYSICAL dimension do not count as anthing more than 1 dimension within the context of Kimball's statement.

For example, if there is an order date, shipping date, and payment date based of the same physical table, DimDate, this is considered one (1) physical dimension with three (3) logical roles.

All of this said, I have seen situations in Healthcare where 20 - 25 physical dimensions have been justified, but, more often than not, if you have more than 15 physical dimensions, chances are you may need to go back to the drawing board.

http://www.kimballgroup.com/data-warehouse-business-intelligence-resources/kimball-techniques/dimensional-modeling-techniques/centipede-fact-table/

Kimball's official quote is this:

"You’re nearing the practical limit on the number of dimensions when you’re
approaching 15 to 18 dimensions. If your design has more, consider
combining correlated dimensions into a single dimension."
Go


Permissions

You can't post new topics.
You can't post topic replies.
You can't post new polls.
You can't post replies to polls.
You can't edit your own topics.
You can't delete your own topics.
You can't edit other topics.
You can't delete other topics.
You can't edit your own posts.
You can't edit other posts.
You can't delete your own posts.
You can't delete other posts.
You can't post events.
You can't edit your own events.
You can't edit other events.
You can't delete your own events.
You can't delete other events.
You can't send private messages.
You can't send emails.
You can read topics.
You can't vote in polls.
You can't upload attachments.
You can download attachments.
You can't post HTML code.
You can't edit HTML code.
You can't post IFCode.
You can't post JavaScript.
You can post emoticons.
You can't post or upload images.

Select a forum

































































































































































SQLServerCentral


Search