How Can I Efficiently Calculate Hamming Distance for SHA256 Hashes in SQL?

Hamming Distance Computation in SQL for Binary Strings

The challenge arises with finding an efficient method to compute the Hamming distance between SHA256 hashes stored in a BINARY(32) column. The straightforward approach of breaking down the binary strings into substrings, casting them to integers, and performing substring-wise Hamming distance calculations seems cumbersome and inefficient.

However, there is an alternative solution that significantly enhances performance. By storing the hash in four BIGINT columns, each containing an 8-byte substring of the original data, it becomes possible to utilize the following function:

<code class="sql">CREATE FUNCTION HAMMINGDISTANCE(
  A0 BIGINT, A1 BIGINT, A2 BIGINT, A3 BIGINT, 
  B0 BIGINT, B1 BIGINT, B2 BIGINT, B3 BIGINT
)
RETURNS INT DETERMINISTIC
RETURN 
  BIT_COUNT(A0 ^ B0) +
  BIT_COUNT(A1 ^ B1) +
  BIT_COUNT(A2 ^ B2) +
  BIT_COUNT(A3 ^ B3);</code>

This function computes the Hamming distance by performing bitwise XOR operations and counting the number of 1s in the results. This approach is considerably faster than the binary string decomposition method.

Additionally, for improved efficiency, it's recommended to use BIGINT columns instead of a BINARY column to store the hash. This alternative method using BIGINTs can result in over 100 times faster execution.

The above is the detailed content of How Can I Efficiently Calculate Hamming Distance for SHA256 Hashes in SQL?. For more information, please follow other related articles on the PHP Chinese website!