i have database structure where all the tables are having two columns for primary key.

for an example the table Author has two columns like AutherId which is a auto increment number and the pc\_id which is unique to that pc the those are the composite keys
for the table. but when it comes to relations i have to define the both columns for
each and every relation. and since im planning to use Docrtine (PHP ORM) it is bit
problematic to use it like that.

so i wonder if i could generate a unique id (combining the pc\_id as well) and use it
as the primary key. 

the php code is like time() . rand(1000,9999) . $pc\_id

so that the id is generated by concatenating time + a random number between 1000 and 9999
and the pc\_id (pc\_id is also a number starting from 1). but this makes a 20 digit number (when the pc\_id is 6 digit) which needs bigint to store

is there a good alternative for this

Regards