View Full Version : Keys - Dimension Lookup/Update
04-12-2006, 07:27 AM
I am trying to use Dimension Update/Lookup and I have put in keys which I think I needed in the Keys area. I just want to get more clarity as to what fields should one put in "Keys". I have also noticed that the more fields you enter the more slow the transformation is gonna be. Why?
If I put no Keys , I get an error with something to do with "AND"
Do you have more explanation around the "Keys"
I am not sure if I put myself across clearly.
04-12-2006, 07:41 AM
The "Keys" are (as specified in the dialog) used to lookup a dimension entry.
They are also refered to as Natural Keys as oposed to Technical Keys or Surrogate Keys.
It is perfectly normal for the lookup to slow down if you just randomly add new fields UNLESS you put an index on those fields to speed up the lookup. (Note that Kettle proposes exactly this if you use the SQL button on the dialog)
You would need some information on slowly changing dimensions to understand all this.
Please search the forum for a list of URLs on Kimball material.
That's as far as I can explain it to you at this point in time.
Hey, looking in the manual and searching on Google with term "Slowly Changing Dimension" might also be a good idea...
04-12-2006, 08:44 AM
My problem is that it loads fine half of the table and not load another half and that when i started thinking maybe that keys could be the unique row identifier. ???
Another problem I now have is that after adding a couple of fields in "Keys" and removing them and putting them back in "Fields", it now suprisingly complaining that they don't exist??
04-12-2006, 11:09 AM
I hope you're not asking me to give you a crash course in multi-dimensional modelling?
>keys could be the unique row identifier. ???
Of course a key is a unique identifier, what else?
Sorry to put it bluntly, but if you don't know what the natural key of a slowly changing dimension is, I can only advise you to stay away from data warehousing until you do know ;-)
>it now suprisingly complaining that they don't exist??
Not surprising at all is it? What is not surpising is that if you change the settings in the Dimension Lookup step and you hit SQL again, you will be served.
Sorry, but I really don't know what you expect from me here: you give me no information whatsoever, no error report, nothing and all you do is complain that something is not working? You got to be kidding me, right?
Hope you *will* find the time to read a good book on the subject, a Slowly Changing Dimension it is very interesting thing to work with ;-)
Over and out, all the best,