How do you use the BINARY_CHECKSUM function to generate a hash value for a binary data?
###### Posted by PaulAnd
Last Updated: June 21, 2024
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.
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