Question on sql.conf -> accounting_start_query <-> accounting_start_query_alt

Hello, to prevent duplicate entries in the radacct table, shouldn't the accounting_start_query be the "UPDATE" query and the accounting_start_query_alt be the "INSERT into" query as it is the case on stop and update. In which case would the accounting_start_query fail and the accounting_start_query_alt work? Could someone point me in the right direction? I know, that freeradius manages handled retransmitted Acct-Requests, so duplicate entries only would show up if at some point it wouldn't remember. I don't know if this is impossible. Thank you. Andreas