通过GROUP BY grouping sets提升数据分组统计效率

使用 GROUPING SETS 的 GROUP BY 子句可以生成一个等效于由多个简单 GROUP BY 子句的 UNION ALL 生成的结果集
示例:(sql server 2008 R2)
创建测试数据库及表并插入测试数据

use master

CREATE DATABASE db_sales

go

use db_sales

go

CREATE TABLE [dbo].[tb_sale](

[id] [int] IDENTITY(1,1) NOT NULL,

[server] [nvarchar](50) NULL,

[pname] [nvarchar](50) NULL,

[pinpai] [nvarchar](50) NULL,

[dates] [smalldatetime] NULL,

[cnt] [int] NULL

) ON [PRIMARY]

go

INSERT INTO [db_ControlManager_ft].[dbo].[test]([server],[pname],[pinpai],[dates],[cnt])

VALUES('A','computer','hp','2012-01-01',1),

('A','computer','hp','2012-01-02',3),

('A','computer','hp','2012-01-03',5),

('A','computer','hp','2012-01-04',1),

('A','computer','hp','2012-01-05',3),

('A','computer','hp','201