SOQL 集計関数の使用 AVG,MAX,MIN

developer.salesforce.comAggregateResult[] groupedResults
  = [SELECT CampaignId, AVG(Amount)
      FROM Opportunity
      GROUP BY CampaignId];
for (AggregateResult ar : groupedResults)  {
    System.debug('Campaign ID' + ar.get('CampaignId'));
    System.debug('Average amount' + ar.get('expr0'));
}