RE: [HACKERS] Standard Deviation function.
От | Stupor Genius |
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Тема | RE: [HACKERS] Standard Deviation function. |
Дата | |
Msg-id | 000001bd9031$1fe5e800$d39daccf@darren обсуждение исходный текст |
Ответ на | Re: [HACKERS] Standard Deviation function. (Bruce Momjian <maillist@candle.pha.pa.us>) |
Ответы |
Re: [HACKERS] Standard Deviation function.
Re: [HACKERS] Standard Deviation function. |
Список | pgsql-hackers |
> > > I really need a Standard Deviation aggregate function... > > > > I thought about this a long time ago and had an idea but never > > got around to trying to implement it. I was going to have some > > functions that worked on a structure of two doubles to track > > the sum and square instead of using only one simple type. > > I remember talking about this to someone, and the problem is that you > needed the average WHILE scanning through the table, which required two > passes, which the aggregate system is not designed to do. I may be > wrong on this, though. I had asked you how to calculate this and the variance early last year. One (I think the variance) was two-pass because of the need for the average, but I thought the StdDev would work with the struct. Been a while and I still haven't configured #(*&^ FreeBSD ppp yet. darrenk
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