Embedded SQL applications must prepare for receiving null values by associating a null-indicator variable with any host variable that can receive a null. A indicator variable is shared by both the database manager and the host application. Therefore, this variable must be declared in the application as a host variable, which corresponds to the SQL data type SMALLINT.
A null-indicator variable is placed in an SQL statement immediately after the host variable, and is prefixed with a colon. A space can separate the null-indicator variable from the host variable, but is not required. However, do not put a comma between the host variable and the null-indicator variable. You can also specify a null-indicator variable by using the optional INDICATOR keyword, which you place between the host variable and its null indicator.
The null-indicator variable is examined for a negative value. If the value is not negative, the application can use the returned value of the host variable. If the value is negative, the fetched value is null and the host variable should not be used. The database manager does not change the value of the host variable in this case.