This function is EXPERIMENTAL. The behaviour of this function, the name of this function, and anything else documented about this function may change in a future release of PHP without notice. Be warned and use this function at your own risk.
ingres_field_nullable() returns TRUE if the field can be set to the NULL value and FALSE if it can't.
index is the number of the field and must be between 1 and the value given by ingres_num_fields().