A NULL value is an undefined value for a field, indicating there is no data available. For sorting purposes, the NULL value's ordinal value depends on its location's definition. The XDB server considers NULL values to be the smallest possible value in all non-EBCDIC environments and with sensitive EBCDIC locations. In all other EBCDIC locations, NULL is sorted as the highest possible value.
Note that NULL values are not the same as blank or zero. NULL values are treated as undefined in mathematical operations, with the result that many expressions involving NULL are in turn resolved as NULL, or undefined.