For nonexistent values, the engine
reads, writes, and updates SAS missing values for the data sources
that implement SAS missing values, which is the SAS data set. For
data sources that do not implement SAS missing values, such as the
third-party databases, a nonexistent value is
-
mapped to an ANSI SQL null value
when writing to the file
-
converted from an ANSI SQL null
value to a SAS missing value when reading from the file.