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.