ah sorry, I was not very precise about "hashed". What I meant (and have done in the past) is to encrypt/decrypt the auto-incrementing ID at the application bou

ah sorry, I was not very precise about "hashed". What I meant (and have done in the past) is to encrypt/decrypt the auto-incrementing ID at the application boundaries. If the OP is really using a one-way hash then yes, you would have to store both IDs.