What is the best practice when implementing equals() for entities with generated ids

If I have a table with columns A, B, C, D
 A: auto-generated id (PK)
 B & C: combination must be unique (these are the columns that actually define identity in the business sense)
 D: some other columns

Now, if I'll create business objects based on this table (e.g. in Java), which one would be a better implementation of the equals() method:

1. define equality based on A
2. define equality based on B and C

or, it wouldn't really matter which of the two I choose.