The BINARY_CHECKSUM function in SQL Server is used to generate a checksum value for a set of input values based on their binary representation. It can be particularly useful for quickly determining whether data has changed, as it produces a hash-like value that can help identify differences between rows.
Here’s how to use the BINARY_CHECKSUM function to generate a hash value for binary data:
Syntax
BINARY_CHECKSUM ( expression [ ,...n ] )
- expression: This is the column or value on which you want to compute the checksum. You can provide multiple expressions to compute a combined checksum.
Example Usage
Here’s a simple example demonstrating how to use BINARY_CHECKSUM with binary data:
1. Creating a Sample Table
First, create a sample table to hold binary data.
CREATE TABLE SampleData (
ID INT PRIMARY KEY,
Data VARBINARY(MAX)
);
2. Inserting Data into the Table
Next, insert some binary data into the table.
INSERT INTO SampleData (ID, Data)
VALUES
(1, CAST('Hello, World!' AS VARBINARY(MAX)),
(2, CAST('Goodbye, World!' AS VARBINARY(MAX));
3. Using BINARY_CHECKSUM
Now, use the BINARY_CHECKSUM function to generate a hash value for the Data column:
SELECT ID, Data, BINARY_CHECKSUM(Data) AS ChecksumValue
FROM SampleData;
Understanding the Output
The output from the above query will show the ID, the original binary Data, and the computed checksum value in a new column ChecksumValue. If the binary data for any row changes, the checksum value will also change, allowing you to detect changes efficiently.
Example for Multiple Columns
If you want to compute a checksum value based on multiple columns, you can provide multiple expressions:
SELECT
ID,
Data,
BINARY_CHECKSUM(ID, Data) AS CombinedChecksum
FROM SampleData;
Notes
- Keep in mind that while BINARY_CHECKSUM is useful for checking modifications, it is not a cryptographic hash function and is not suitable for security purposes.
- Collisions (different data producing the same checksum) are possible, so it shouldn’t be solely relied upon for unique identification of data.
- If you require stronger integrity checks and uniqueness guarantees, consider using cryptographic hash functions like HASHBYTES.
Conclusion
Using BINARY_CHECKSUM is straightforward and provides an efficient way to generate a hash value for binary data or combinations of data. It is a quick method for tasks such as comparisons and detecting changes in databases.