The DataServer supports null values. Procedures that use a null value behave exactly as they do when accessing an Unknown value (?) in an OpenEdge database, except for one difference—you cannot compare a field to the Unknown value (?) if the field is not allowed to hold the Unknown value (?) (i.e., is not null-capable). For example, if the custnum field is not null-capable, the following statement fails at run time:

FIND customer WHERE customer.custnum NE ?

A column that is not null-capable is marked "mandatory" in the schema holder.

In a DataServer application, you assign the Unknown value (?) to a column by using the question mark operator (?), which the DataServer translates to the appropriate null-value representation. For example, the following procedure assigns the Unknown value (?) to the address2 field of the customer table:

FIND FIRST customer.
customer.address2 = ?.