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List:       mysql
Subject:    RE: harmonic mean in SQL
From:       "Jay Blanchard" <jblanchard () pocket ! com>
Date:       2010-10-22 11:20:01
Message-ID: 31454D514FF9A949B1FDFE294D5D1D8095DDE7 () ygex01wal ! onecall ! local
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[snip]
The mathematical way to add two "partial" harmonic means to generate new
harmonic mean is:

Let X1  , X2 be two harmonic means on different rollup rows, generated
using
n1 and n2 # of facts respectively.

The combined harmonic mean would be:

(n1 + n2)/( n1/x1 + n2/x2)

If you have experience with computing harmonic mean in SQL, please
share.
[/snip]

Unless I am misunderstanding your question the simplest method would be;

SELECT ((n1 + n2)/(n1/x1 + n2/x2)) AS "Harmonic Mean" 

...without knowing the structure of the data. If X1 and X2 live on 2
different rows you could write a stored procedure to retrieve the
relevant data and produce an output.

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