mysql数据库:
select
if(avg(cai.conversionsrate) is null,0,avg(cai.conversionsrate))
as conversionsrate
from campaign_info cai
where inserttime between '2011-02-01' and '2011-02-04' and googlecampaignid=23331401
ms-sqlserver数据库
/*ms-sqlserver去除null值*/
select isnull(avg(cai.conversionsrate),0)
as conversionsrate
from campaign_info cai
where inserttime between '2010-02-11' and '2011-01-23' and googlecampaignid=42722951