When/Why does Oracle adds NaN to a row in a database table

Question

I know that NaN stands for Not a Number. But, I have trouble understanding when and why Oracle adds this to a row.

Is it when it encounters a value less than 0 like

Answer 1

Nope <=0 is still a number so not quite. NaN (or infinity) are special values that the DB uses to keep it's sanity when dealing with non-computable numbers (+-∞, or simply something that is not a number). Here's some code:

DECLARE
  l_bd_test   binary_double;
  l_int_test  INTEGER;
BEGIN
  l_bd_test   := 'NAN';
  l_int_test  := 0;
  IF l_bd_test IS NAN THEN 
    DBMS_OUTPUT.PUT_LINE(l_bd_test || ' IS NAN');
  ELSE
    DBMS_OUTPUT.PUT_LINE(l_bd_test || ' IS A #');
  END IF;
  IF l_int_test IS NAN THEN 
    DBMS_OUTPUT.PUT_LINE(l_int_test || ' IS NAN');
  ELSE
    DBMS_OUTPUT.PUT_LINE(l_int_test || ' IS A #');
  END IF;
END;
/

Substitute NAN for INFINITY or even negate it and see the results.