Use the NULL_NUMERIC_WRITE variable to indicate how SQL NULLs in numeric data should be translated into COBOL data. For data returned to the COBOL files (WRITEs), indicate whether the NULLs in numeric data should be interpreted as SPACES, LOW-VALUES, or zero. Valid values are:
Numeric fields that take the form of one of the computational types further complicate the situation. For most comp fields, LOW-VALUES and SPACES are valid values. See the configuration variable NULL_NUMERIC_READ for examples. In order to prevent erroneous information being written to the COBOL data files by the insert of a NULL value, tables created with comp fields that could be misinterpreted are created with the NOT NULL constraint on these columns.
The following describes the null ability of numeric columns:
Numeric : NULL
COMP : NOT NULL
COMP-1 : NOT NULL
COMP-2 : NULL
COMP-3 : NOT NULL
COMP-4 : NOT NULL
COMP-5 : NOT NULL
COMP-6 : NOT NULL
The bottom line is that the columns whose underlying data types require NOT NULL are required and must have a value specified in them for a successful insert or update.