In DB2 host variable handling, what do null indicator values of -1, 0, and -2 generally mean for a column?

Introduction / Context:
When using embedded SQL with host variables, DB2 uses null indicator variables to represent whether a column is null or if special conditions occurred during data transfer. Understanding indicator values such as -1, 0, and -2 is essential for correctly handling nulls and truncation errors in application code.

Given Data / Assumptions:

• An application program uses host variables and optional indicator variables for DB2 columns.
• Indicator variables are defined as integer types and associated with specific host variables.
• DB2 sets indicator values when fetching data and reads them when inserting or updating data.

Concept / Approach:
The basic convention is that an indicator of 0 means the column is not null and the host variable contains valid data. An indicator of -1 means the column value is null. An indicator of -2 is used in some cases to signal that data has been truncated or that some other exceptional condition occurred when moving data between DB2 and the host program. The correct option must capture these meanings rather than inventing unrelated semantics.

Step-by-Step Solution:
Step 1: Recall the general rule: negative indicator values usually denote special conditions, such as null or data issues. Step 2: Recognize that -1 is the standard indicator meaning that the column is null. Step 3: Remember that 0 indicates a normal non null value in the host variable. Step 4: Understand that -2 is used to indicate a truncated value or another error during assignment, which the program should handle. Step 5: Choose the option that describes these three conditions accurately and concisely.

Verification / Alternative check:
Sample programs and DB2 documentation illustrate indicator handling by showing code that checks for -1 before using a host variable and logs or handles -2 as an error or warning about truncation. Observing such patterns in real systems confirms the meanings of -1, 0, and -2 as summarized in option A.

Why Other Options Are Wrong:
Option B is wrong because indicators do not directly instruct DB2 to update, ignore, or delete rows; they describe value state, not operations.
Option C is wrong because access control is handled through privileges and security, not through null indicator values.
Option D is wrong because key roles such as primary or foreign keys are defined in schema definitions, not represented by indicator values at run time.

Common Pitfalls:
A common mistake is to ignore indicator variables entirely and assume every column is non null, which can cause program failures or misinterpreted results. Another pitfall is mishandling -2, treating it the same as -1, and losing track of truncation problems. Proper coding practice is to always check indicators for negative values and handle them according to application requirements.

Final Answer:
For DB2 null indicators, indicator -1 means the column value is null, 0 means it is not null, and -2 indicates a truncated or invalid value situation.