In SQL Server, the ROWVERSION data type (previously known as TIMESTAMP) is primarily used for concurrency control. It provides a unique binary number that is automatically generated and updated every time a row is inserted or updated in a table. This makes it useful for ensuring that updates to a row are based on the most current data, providing a mechanism to detect changes and handle concurrency issues.
Using ROWVERSION for Concurrency Control
Here’s a step-by-step explanation of how to use the ROWVERSION data type for concurrency control:
1. Create a Table with a ROWVERSION Column:
You need to define a table that includes a ROWVERSION column. This column will automatically generate a unique binary value for every row.
CREATE TABLE Products (
ProductID INT PRIMARY KEY,
ProductName NVARCHAR(100),
Price DECIMAL(10, 2),
LastUpdated ROWVERSION
);
2. Insert Data:
When inserting records into the table, the LastUpdated column will automatically receive a unique ROWVERSION value.
INSERT INTO Products (ProductID, ProductName, Price)
VALUES (1, 'Product A', 10.00);
3. Read Data:
When reading records, you will also retrieve the ROWVERSION value.
SELECT ProductID, ProductName, Price, LastUpdated
FROM Products
WHERE ProductID = 1;
4. Implementing Update Logic:
When updating data, you should include the current ROWVERSION value in your WHERE clause to ensure that the data has not changed since it was read.
DECLARE @CurrentVersion ROWVERSION;
SELECT @CurrentVersion = LastUpdated
FROM Products
WHERE ProductID = 1;
UPDATE Products
SET Price = 12.00
WHERE ProductID = 1 AND LastUpdated = @CurrentVersion;
5. Checking for Concurrency Conflicts:
After attempting the update, you can check how many rows were affected. If no rows were affected, it means that the ROWVERSION has changed, indicating that another transaction has modified the row since it was last read.
IF @@ROWCOUNT = 0
BEGIN
PRINT 'Concurrency conflict detected. The record has been modified by another user.';
END
ELSE
BEGIN
PRINT 'Update successful.';
END
6. Handling Concurrency Conflicts:
You will need to decide how to handle concurrency conflicts based on your application's needs. This might include notifying the user, allowing them to merge changes, or retrying the update operation.
Conclusion
Using the ROWVERSION data type in SQL Server is an effective way to manage concurrency in applications that require high data integrity. It allows developers to detect when data has changed between the time it was read and the time it was updated, enabling better control over concurrent updates and conflict resolution.