数据库转化null值

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