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?
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.