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From:Jules Bean Date:April 21 1999 9:39am
Subject:Re: bc math support in MySQL?
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On Wed, 21 Apr 1999, Tobias Rischer wrote:

> On fixed point numbers, it was said that:
> > Essentially, this should be implemented simply as an integer, with an
> > automatic scale on the IO routines.
> > 
> > Alternatively, simply use an integer, and do the scaling in your
> > middleware! ;)
> Just to keep people from stumbling, I'd like to add: 
> This is good advice, as long as the only calculations done on the
> integers *as integers* (e.g. in a SELECT expression) are + and -
> operations.  It will wonderfully fail for "<fixed> * <fixed>" or
> "<fixed> / <fixed>"; these operations need to know about the implied
> scaling.
> It is ok to do "<int> * <fixed>", "<fixed> / <int>" etc.
> 	Tobias
> Personal Statement: 
> I like the idea of fixed point numbers as the underlying data type for
> DECIMAL(m,n) [or was it NUMERIC?], maybe even a BCD type.  

I can't think of any advantages to BCD at all.. someone enlighten me..

> I'm not much of a business man, but even I wouldn't like my bank to
> arbitrarily toggle the last digits of my bank account and explain that
> with floating point anomalies caused by the exact sequence of my earning
> and spending money. (I can almost see them telling me I should never
> look for exact equality in an account balance, but rather use some
> appropriate Epsilon!  :-)

Yup.  The appropriate epsilon is one half of a cent, in general.  Someone
told me (I can't substantiate this myself) that most bank accounts
automatically round to the nearest penny/yen/pfennig at the close of
business each day.


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|  Julian Bean   | jmlb2@stripped        |  TW9 2TF *UK*       |
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bc math support in MySQL?jkraai20 Apr
  • Re: bc math support in MySQL?Jules Bean20 Apr
    • Re: bc math support in MySQL?Tobias Rischer21 Apr
      • Re: bc math support in MySQL?Tobias Rischer21 Apr
    • Re: bc math support in MySQL?Tobias Rischer21 Apr
      • Re: bc math support in MySQL?Jules Bean21 Apr
    • Re: bc math support in MySQL?Fred Read21 Apr
Re: bc math support in MySQL?jkraai20 Apr