MySQL将varchar二进制表示字段转换为二进制以使用bit_count进行汉明距离计算

Question

I've a db table with a varchar(64) field to store PHashing data, as 64 chars (1's and 0's ascii characters). I need to calculate hamming distance with a test hasta, and it seems that the most efficient way to do is using mysql bit_count function. The problem is that I haven't found any way to convert/cast/whatever the hash field in order to be interpreted as a byte(8) instead of varchar(64). Like:

> select hash from data;
"0000000101100111111100011110000011100000111100011011111110011011"
> select convert_to_binary(hash) from data;
0b0000000101100111111100011110000011100000111100011011111110011011

I cannot alter the data and convert all previous data into a binary field. Is there any way to force mysql to re-interpret a field as a literal, or any other alternative solution?

Answer 1

I think you should be able to use it like this:

SELECT BIT_COUNT(CAST(hash AS BINARY)) FROM data;

Use CAST to convert the field to BINARY and pass the result to BIT_COUNT . Casting the field hash to binary will turn it into a string with the binary data type, but BIT_COUNT is able to handle that.

Answer 2

Working code:

SELECT BIT_COUNT( CONV( hash, 2, 10 ) ^ 
0b0000000101100111111100011110000011100000111100011011111110011011 )