About JPA TABLE_PER_CLASS and sub entity id

Question

In the TABLE_PER_CLASS mapping,

does the sub entity id need be unique in all kind of sub entity instance

for example:
Employee : 1,2,3,4,5,6
Sales: 1,3,5
Developer: 2,4,6

or can be unique in it's table:

Employee : 1,1,2,2,3,3
Sales: 1,2,3
Developer: 1,2,3

I'm using MySQL, I have to create a table:hibernate_sequences to maintain the id unique in all sub enities, is there any information about this table's specification ?

I have googled, but cannot find information about this.

Answer 1

In the TABLE_PER_CLASS ( http://docs.oracle.com/javaee/6/tutorial/doc/bnbqn.html#bnbqs ) mapping each entity has its own table, so the ids dont have to be unique in the whole entity hierarchy. They have to be unique only in its table (so your second example is right)