The null-indicator variable is examined for a negative
value. If the value is not negative, the application can
use the returned value of the host variable. If the value
is negative, the fetched value is null and the host
variable should not be used. The database manager does not
change the value of the host variable in this case.
If the database configuration parameter dft_sqlmathwarn is
set to 'YES', the null-indicator variable value may be -2.
This value indicates a null that was either caused by
evaluating an expression with an arithmetic error, or by an
overflow while attempting to convert the numeric result
value to the host variable.