Release 10.1A: OpenEdge Data Management:
DataServer for Microsoft SQL Server

> ## Unknown value (?)

> 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 `cust-num` field is not null-capable, the following statement fails at run time:

>     FIND cust WHERE cust-num <> ?

> 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.
>     address2 = ?.

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