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From Daniel John Debrunner <...@debrunners.com>
Subject Re: derby's function system
Date Thu, 03 Feb 2005 18:40:04 GMT
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> shahbaz chaudhary wrote:

>>
>>Regarding aggregators, it looks like they are implemented by operating
>>on two values at a time (looking at SumAggregator): a value to be
>>added and a value which was populated previously (presumably
>>containing aggregate result of column already traversed).

So to be a little clearer, the aggregator operates on a single incoming
 value and a context object specific to the aggregator function. This
context object is where you would maintain your list of previous values
if required.

Eg. for the max aggregator the context object would simply contain the
current maximum value, for a top-three average it would maintain the top
three values and calculate the final value at finish time.

Dan.
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