In SQL Server, what rules apply when using the ROWGUIDCOL property to define a column that represents a globally unique identifier in a table?

Introduction / Context:
SQL Server provides the ROWGUIDCOL property to mark a column that stores a globally unique identifier, often used for replication or as a surrogate key in distributed systems. Interview questions may ask about the specific rules for using this property because it helps distinguish between logical labeling and physical constraints. Knowing what ROWGUIDCOL does and does not do prevents design mistakes in databases that need unique identifiers across multiple servers.

Given Data / Assumptions:
We are working with Microsoft SQL Server tables.ROWGUIDCOL is applied to a single column to indicate that it represents a row level global identifier.The typical data type is uniqueidentifier, which stores globally unique values.We focus on the rules and limitations of the ROWGUIDCOL property itself.

Concept / Approach:
ROWGUIDCOL is a column property that marks a column as the logical globally unique identifier for the row. SQL Server uses this flag in some features such as replication and certain system functions. However, it does not automatically generate values or enforce uniqueness. The column must have the data type uniqueidentifier and there can be at most one ROWGUIDCOL column in a table. Developers usually combine this property with a default constraint that calls NEWID or NEWSEQUENTIALID to populate values and may also define a unique index or primary key constraint to enforce uniqueness.

Step-by-Step Solution:
Step 1: Recall that ROWGUIDCOL is a property, not a data type, and it is meant for columns that hold globally unique identifiers.Step 2: Remember that SQL Server requires the column to have the uniqueidentifier data type when ROWGUIDCOL is used.Step 3: Note that each table can have only one column marked as ROWGUIDCOL.Step 4: Understand that the property alone does not create primary key or unique constraints; those must be defined separately.Step 5: Option A is the only one that states these rules correctly, so it is the correct choice.

Verification / Alternative check:
Documentation shows syntax examples where tables are created with a uniqueidentifier column, a default of NEWID, and the ROWGUIDCOL property. It also explains that a table can have only one such column and that the property is mainly a marker used by certain features. There is no automatic creation of foreign keys or primary keys just because the property is present. This aligns with option A and conflicts with the exaggerated claims in other options.

Why Other Options Are Wrong:
Option B incorrectly claims that any data type can be used and that each table must have exactly two ROWGUIDCOL columns, which violates SQL Server rules. Option C suggests that ROWGUIDCOL converts an integer into a foreign key for every table, which is completely incorrect. Option D restricts ROWGUIDCOL to image data and says it forces non nullability, both of which are false. Option E says it is used only for text indexing and has no relation to unique identifiers, which again misrepresents the property purpose.

Common Pitfalls:
Developers sometimes assume that marking a column as ROWGUIDCOL automatically guarantees uniqueness, which can lead to duplicate values if proper constraints are not added. Another pitfall is using the property inconsistently across tables in replicated environments, which can complicate troubleshooting. Some projects also misuse uniqueidentifier columns when simpler integer keys would suffice, leading to larger index sizes. Clear understanding of ROWGUIDCOL as a descriptive marker, not a full constraint mechanism, helps avoid these issues.

Final Answer:
The correct answer is: The column must be of type uniqueidentifier, only one ROWGUIDCOL column is allowed per table, and the property itself does not enforce uniqueness or primary key status.