How to get the Failure Record Ids From Database.SaveResult[]

if You Need To check The Success Record Ids and Failure Record Ids.
If DML Operation is Success Will Get Record Id From Database By Using getId()  Method in Database.SaveResult Class.
If any DML Operation Fails while Processing The Record no way to Get the Failure Record Id in
Database.Error Class

To Get the Failure Record Id, We can use List index Property to get the Id of the failed record.

Check Bellow code

list<Account> lstAccToUpdate = new list<Account>();
list<Account> lstAccounts = [Select id, Name, Industry From Account limit 10];
for(Account aIterator : lstAccounts) {
    aIterator.Industry = 'Banking';
    lstAccToUpdate.add(aIterator);
}
if(lstAccToUpdate != null && !lstAccToUpdate.isEmpty()) {
    Database.SaveResult[] result = Database.update(lstAccToUpdate,false);
    for(Integer i=0; i < result.size(); i++) {
        if(result.get(i).isSuccess()) {
            System.debug('Records are updated Successfully');
        } 
        else if(!result.get(i).isSuccess()) {
            Database.Error errors =  result.get(i).getErrors().get(0);
            System.debug('Error Occurs While Processing The Record'+errors.getMessage());
            System.debug('Failure Record Ids While Updating'+result.get(i).Id);
        }
    }
}

Let us know if you have any queries.
Happy Learning!!