global class UpdateEventScore implements Database.Batchable<sObject> {

    global Database.QueryLocator start(Database.BatchableContext bc) {
        // collect the batches of records or objects to be passed to execute
        return Database.getQueryLocator(
             'Select Contact.Account.ID' +
             'from CampaignMember' +
             'WHERE Campaign.StartDate = LAST_N_DAYS:365' +
             'AND status = 'Attended' ORDER BY Campaign.StartDate'
        )
    }
    global void execute(Database.BatchableContext bc, List<P> records){
        // process each batch of records
    }
    global void finish(Database.BatchableContext bc){
        // execute any post-processing operations
    }
}

global class UpdateEventScore implements Database.Batchable<sObject> {

    global Database.QueryLocator start(Database.BatchableContext bc) {
        // collect the batches of records or objects to be passed to execute
        return Database.getQueryLocator([
          SELECT Id FROM Account WHERE Id IN (
            SELECT Account__c
            FROM CampaignMember
            WHERE Campaign.StartDate = LAST_N_DAYS:365 AND
                  Status = 'Attended'
        ]);
    }
    global void execute(Database.BatchableContext bc, List<Account> records){
        // process each batch of records
    }
    global void finish(Database.BatchableContext bc){
        // execute any post-processing operations
    }
}