re: Debunking Kimball Effective Dates
Hi AaronBertrand,In reference to I/O being expensive. Using the proposed logic of having to join back to the table to find the successor record, ir going to cost you allot more than the storage of the...
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No problem. The thing people miss is that even in a denormalized DM, speed is a *secondary* consideration. It's easy to get fast results if you don't care how wrong they are. In every DM (at least...
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Hey Mike,Thanks for the replies.I guess it comes down to making the trade-off between perf and accuracy - I seem to spend my whole work life wondering exactly where to make that trade-off, y'know. In...
View Articlere: Debunking Kimball Effective Dates
@JaggedEdge - Don't be skurred.If GROUP BY skurrs you, then try a CTE with a windowing function (ROW_NUMBER) instead.Not sure why you'd find GROUP BY skurry. If something were to keep me up at night...
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Using Jamie's method of storing just a start date you can *accurately* infer the end dates. As has been pointed out already here, accurately enforcing end dates when you store the start and end dates...
View ArticleMind that collation : SSAS
I’ve been using Analysis Services a lot lately in my current day job and recently encountered an issue
View Articlere: Debunking Kimball Effective Dates
Wow, that enormous group by does not look very appealing. Not only is there another layer of abstraction, but when columns get added I have to update a view, and the group by is gonna make it crawl.
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Stuart,All good points. I'd like to ask you something about the following:"the ETL process should not govern the design of the warehouse based on updates"Is that still the case even if the columns in...
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I don't like the view option. Firstly, this is larger overhead than just getting the data directly from the table. Secondly, the ETL process should not govern the design of the warehouse based on...
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I will second the suggestion that this technique is not suitable for cases where dimensions are expired when no facts arrive (monthly snapshot paradigm, for example). In this case, there is no place...
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Hi Peter,Your 2 cents are very welcome :)"In your reply to my post you referred to the point that you want to avoid storing data twice. Does that mean you are snowflaking your dimensional model in...
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Jamie,In your reply to my post you referred to the point that you want to avoid storing data twice. Does that mean you are snowflaking your dimensional model in order to avoid doing that?The whole...
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CVarela,No, it wasn't done to make a point - it was done cos I'm an idiot! :)In other words, it didn't deliberately join on [Name], that was a mistake. Indeed the join *should* be done on [NId].I've...
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Pete, space is cheap but I/O is not... even on high performance EMC2 Clariions we are constantly hitting bottlenecks in I/O. When I can save 4 or 8 bytes per row, I do it.
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This is good stuff man.I've done this kind of optimization before, but I've never taken the time to document it such as you have in this well-written article.Who cares about the space savings of a date...
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Good points Jamiet but (there's always one isn't it ;) )Why do you LEFT JOIN using the C.Name instead of CNId? Joining by C.Name would only work if you replicate the changes to all records when it...
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Jamie-Thanks for the post (and the ensuing debate). I think there may be some situations where this technique is better overall, but I'd have to guess that most situations would be best tackled with...
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Michelette,Throughout the years I have seen that so many database designers have head-in-the-coulds notions that they can forget all aspects of physical modelling. It seems obvious to me this is mainly...
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Jamie, Good article. I'm not a DBA, but rather a programmer and have never read Kimball nor heard of Kimball. However, one thought occurs to me as we were attempting to model something like this....
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Jamie,Start and end dates are not just to make the ETL easier, it also helps to answer business questions related to the state of a dimension at a particular time (how many children did Henry have on...
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