min() and NaN

Hi,

I have a table containing a double precision column. That column 
contains at least one judiciously placed NaN.

I'd expect the aggregate function min() to return the minimum, valid 
numeric value.  Instead, it seems to return the minimum value from the 
subset of rows following the 'NaN'.

What's going here?  What should I expect the aggregate function min() to 
return in this case?  And why?

Any help is appreciated,
Mike


testdb=> \d min_with_nan
       Table "public.min_with_nan"
  Column |       Type       | Modifiers
--------+------------------+-----------
  col1   | double precision |

testdb=> select * from min_with_nan ;
  col1
-------
  3.141
  2.718
    NaN
     10
(4 rows)

testdb=> select min(col1) from min_with_nan ;
  min
-----
   10
(1 row)

testdb=> select min(col1) from min_with_nan where col1 != 'NaN';
   min
-------
  2.718
(1 row)