The Secure Hash Algorithm (SHA) is a group of cryptographic hash algorithms that generate a fixed-size hash value from input data. SQL Server includes operations for dealing with cryptographic hashes, such as the SHA algorithm. The SHA algorithms can be used in SQL Server in the following ways.

SHA-1
The HASHBYTES function in SQL Server allows you to compute a SHA-1 hash value for a specified input string. Here's an illustration.

DECLARE @InputString NVARCHAR(100) = 'Hello, world!';
DECLARE @HashValue VARBINARY(20);
SET @HashValue = HASHBYTES('SHA1', @InputString);
SELECT @HashValue AS SHA1Hash;

SHA-256
SQL Server also supports the SHA-256 hash algorithm using the HASHBYTES function. SHA-256 produces a 256-bit hash value.
DECLARE @InputString NVARCHAR(100) = 'Hello, world!';
DECLARE @HashValue VARBINARY(32);
SET @HashValue = HASHBYTES('SHA2_256', @InputString);
SELECT @HashValue AS SHA256Hash;

SHA-512
SQL Server also supports the SHA-512 hash algorithm, which generates a 512-bit hash value.
DECLARE @InputString NVARCHAR(100) = 'Hello, world!';
DECLARE @HashValue VARBINARY(64);
SET @HashValue = HASHBYTES('SHA2_512', @InputString);
SELECT @HashValue AS SHA512Hash;

Please note that the HASHBYTES function returns the hash value as a VARBINARY type. If you want to display the hash value as a string, you can use the CONVERT function to convert it to a hexadecimal representation.
SELECT CONVERT(NVARCHAR(MAX), @HashValue, 2) AS HexadecimalHash;

Keep in mind that SHA-1 is considered weak and insecure for many cryptographic purposes due to vulnerabilities discovered over time. SHA-256 and SHA-512 are currently more secure options.

When to use SHA hashes?
Storing passwords: Never store plain text passwords. Instead, store a SHA2 hash which cannot be reversed. When a user logs in, hash their entered password and compare it to the stored hash. Data integrity: Compute a SHA hash of a data set and store it. To verify data has not changed, recompute the hash and compare it to the stored value. Changed data will result in a mismatched hash.
Generate unique values: The unique SHA hash can be used to generate unique IDs, encryption keys, etc.
Verify file downloads: The host can provide a SHA hash of the file for the client to verify the downloaded file contents match the expected hash.

How to use SHA in SQL Server?
Use the HASHBYTES() function to generate a SHA hash in T-SQL code.
HASHBYTES('SHA2_512', 'SomeStringData')
The ALGORITHM parameter takes 'SHA1' 'SHA2_256' or 'SHA2_512'.
To hash passwords, use a salt value to protect against rainbow table attacks. Concatenate with a random unique salt before hashing.
DECLARE @Salt varchar(20) = 'RandomSaltString'

SELECT HASHBYTES('SHA2_512', 'MyPassword' + @Salt)

When checking hashes for data integrity, store the expected hash value alongside the data. Recompute the hash periodically and compare.

Benefits of Using SHA Hashing

• One-way hash allows securely storing sensitive data like passwords.
• A small change in input drastically changes the output hash, allowing the detection of altered/corrupted data.
• Hashing data into fixed-length output allows for easier comparisons and indexing.
• SHA is optimized for speed and designed to be cryptographically secure.

SQL Server's SHA hash functions are most useful for securely storing sensitive data, validating data integrity, and generating unique fingerprint values of data.

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