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Spurious constants
Posted: Tue Dec 14, 2004 8:08 am
by PhilHibbs
ProfileStage seems to be a little over-zealous at identifying columns as constant. For instance, I have a table with nearly 600,000 rows, and all but 20 of these rows have zero in a particular field. ProfileStage says this is 100% constant. Is this supposed to happen? What is the threshhold for constancy?
Posted: Tue Dec 14, 2004 8:16 am
by chulett
Sorry, somewhat spurious comment here...
What would you rather it say? 99.9967% constant? (I left off a few 6s, btw) I'm guessing it decided to round it up for you.
Or are you wondering if there is a way to
not identify zero as a constant value? To treat it more like a null or unknown value, perhaps?
Posted: Tue Dec 14, 2004 8:48 am
by PhilHibbs
chulett wrote:Sorry, somewhat spurious comment here...
What would you rather it say? 99.9967% constant? (I left off a few 6s, btw) I'm guessing it decided to round it up for you.
Or are you wondering if there is a way to
not identify zero as a constant value? To treat it more like a null or unknown value, perhaps?
The difference between 99.9967% and 100% is much bigger than the difference between, say, 50% and 75%.
My colleague has resolved the problem by looking at the cardinality instead, a cardinality of 1 indicates a true constant field.