Do not confuse the SQL concept of NULL with the C-language constant of the same name. In the SQL language, NULL represents either an unknown attribute or inapplicable information. The C-language constant represents a pointer value that does not point to a memory location.

When NULL is used in the SQL Anywhere documentation, it refers to the SQL database meaning given above. The C language constant is referred to as the null pointer (lowercase).

NULL is not the same as any value of the column's defined type. To pass NULL values to the database or receive NULL results back, you require something beyond regular host variables. Indicator variables serve this purpose.

 Using indicator variables when inserting NULL

EXEC SQL BEGIN DECLARE SECTION;
short int employee_number;
char employee_name[50];
char employee_initials[6];
char employee_phone[15];
a_sql_len ind_phone;
EXEC SQL END DECLARE SECTION;
/* set values of empnum, empname,
   initials, and homephone */
if( /* phone number is known */ ) {
   ind_phone =  0;
} else {
   ind_phone = -1; /* NULL */
}
EXEC SQL INSERT INTO Employee
   VALUES (:employee_number, :employee_name,
   :employee_initials, :employee_phone:ind_phone );

 Using indicator variables when fetching NULL