Greenplum
has a special value called NULL. A Greenplum NULL value means an absence
of information and is analogous to a SAS missing value. When
SAS/ACCESS
reads a Greenplum NULL value, it interprets it as a SAS missing value.
When loading SAS tables from Greenplum sources,
SAS/ACCESS stores
Greenplum NULL values as SAS missing values.
In Greenplum tables,
NULL values are valid in all columns by default. There are two methods
to define a column in a Greenplum table so that it requires data:
-
Using SQL, you specify a column
as NOT NULL. This tells SQL to allow only a row to be added to a table
if a value exists for the field. Rows that contain NULL values in
that column are not added to the table.
-
Another approach is to assert NOT
NULL DEFAULT. For more information, see the
Greenplum Database
Administrator Guide.
Once you know whether
a Greenplum column enables NULLs or the host system supplies a default
value for a column that is defined as NOT NULL WITH DEFAULT, you can
write selection criteria and enter values to update a table. Unless
a column is defined as NOT NULL or NOT NULL DEFAULT, it enables NULL
values.
To
control how the DBMS handles SAS missing character values, use the NULLCHAR= and NULLCHARVAL= data set options.