Question

I have a simple question which occured when I wanted to store the result of a SHA1 hash in a MySQL database:

How long should the VARCHAR field be in which I store the hash’s result?

Answer 1

I would use VARCHAR for variable length data, but not with fixed length data. Because a SHA-1 value is always 160 bit long, the VARCHAR would just waste an additional byte for the length of the fixed-length field.

And I also wouldn’t store the value the SHA1 is returning. Because it uses just 4 bit per character and thus would need 160/4 = 40 characters. But if you use 8 bit per character, you would only need a 160/8 = 20 character long field.

So I recommend you to use BINARY(20) and the UNHEX function to convert the SHA1 value to binary.

I compared storage requirements for BINARY(20) and CHAR(40).

CREATE TABLE `binary` (     `id` int unsigned auto_increment primary key,     `password` binary(20) not null ); CREATE TABLE `char` (     `id` int unsigned auto_increment primary key,     `password` char(40) not null ); 

With million of records binary(20) takes 44.56M, while char(40) takes 64.57M. InnoDB engine.