Re: avg() from multiple columns

Jason Tan wrote:
  >
  >
  >If you want row by row averages try this:
  >
  >select (col1+col2+col3)/3 from table;
  >
  >If you wnat to average several columns over the whole table this seems to
  >work:
  >
  >select avg(col1+col2+col3) from table;

Watch out for NULL values when doing this.  x + x + NULL = NULL, not 2x

You might do better to do:

  SELECT avg(col1) + avg(col2) + avg(col3)

or

  SELECT avg(COALESCE(col1, 0) + COALESCE(col2, 0) + COALESCE(col3,0))

(the two are not equivalent).

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Oliver Elphick                                Oliver.Elphick@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
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