Legacy database 2 tables:
table A (a materialized view): col-a1, col-a2, ...
table B: id, col-b1, ...

Question:
col-b1 contains combined values of col-a1 and col-a2
for some rows, col-b1's values reference to col-a1; for other rows, col-b1's values reference to col-a2

How should I do hibernate entity mapping with annonation? I need col-a1 be primary key sometime to join col-b1, and col-a2 be primary other times to join col-b1. Is it possible?

I don't want to create 2 sets of entities (i.e Entity_A1, col-a1 PK --> Entity_B1; Entity_A2 col-a2 PK --> Entity_B2)
thanks

Try using @JoinColumnOrFormula as indicated in this StackOverflow answer.