sql 聚合数据， 求一年中每月的销量和

思路 ： 先求出 每个月 的销售量 然后累加起来

SELECT   CONVERT(varchar(7), CreateDate, 120) AS num, CONVERT(varchar(4), CreateDate, 120) AS num2, PrePrice
                 FROM      dbo.SER_Services
                 WHERE  (CONVERT(varchar(4), CreateDate, 120) = CONVERT(varchar(4), '2018', 120)）

将相同月份的数据求和

SELECT   num AS Date, COUNT(num2) AS SerBills, SUM(PrePrice) AS SumPrice
			FROM    
  (SELECT   CONVERT(varchar(7), CreateDate, 120) AS num, CONVERT(varchar(4), CreateDate, 120) AS num2, PrePrice
            FROM      dbo.SER_Services
 WHERE  (CONVERT(varchar(4), CreateDate, 120) = CONVERT(varchar(4), '2018', 120))) AS a  GROUP BY num

将数据 汇总