uniqid as Primary Key

[admin]

I'm defining tables with md5(uniqid(rand())) (varchar 32) as Primary Key instead integer auto_increment.

I pass this id's in URL.
product.php?id=asdirjksndfj34dkwrejr...
instead
product.php?id=3

So i do this for security reason.

Is this an important lost of efficiency in select query's ??

Thanks


Sorry for my bad english.