统计每天订单量
需求很简单,就是统计一年以来每天的订单量,一开始以为很简单,group by 日期下就好了,但发现很多天的订单量是0,于是那天就没有统计进去,求一个方法,如果订单量是0,那也要显示出来,日期,订单量(0) group?by? group?by 日期
[解决办法]
这里需要一个参照表，这个表最少包含一列连续的没有截断的日期，然后假设这个表为a
select a.日期,isnull(b.订单量,0) 订单量
from a left join (你一开始的语句) b on a.日期=b.日期
[解决办法]

 CREATE   TABLE   [dbo].[time_dimension]   (
      [time_id]   [int]   IDENTITY   (1,   1)   NOT   NULL   ,
      [the_date]   [datetime]   NULL   ,
      [the_day]   [nvarchar]   (15)   NULL   ,
      [the_month]   [nvarchar]   (15)   NULL   ,
      [the_year]   [smallint]   NULL   ,
      [day_of_month]   [smallint]   NULL   ,
      [week_of_year]   [smallint]   NULL   ,
      [month_of_year]   [smallint]   NULL   ,
      [quarter]   [nvarchar]   (2)   NULL   ,
      [fiscal_period]   [nvarchar]   (20)   NULL
)   ON   [PRIMARY]

   
DECLARE   @WeekString   varchar(12),
@dDate   SMALLDATETIME,
@sMonth   varchar(20),
@iYear   smallint,
@iDayOfMonth   smallint,
@iWeekOfYear   smallint,
@iMonthOfYear   smallint,
@sQuarter   varchar(2),
@sSQL   varchar(100),
@adddays   int
   
SELECT   @adddays   =   1   --日期增量（可以自由设定）
SELECT   @dDate   =   '01/01/2002 '   --开始日期
   
WHILE   @dDate   <   '12/31/2004 '     --结束日期
BEGIN
   
      SELECT   @WeekString   =   DATENAME   (dw,   @dDate)
      SELECT   @sMonth=DATENAME(mm,@dDate)
      SELECT   @iYear=   DATENAME   (yy,   @dDate) 
 
      SELECT   @iDayOfMonth=DATENAME   (dd,   @dDate)
      SELECT   @iWeekOfYear=   DATENAME   (week,   @dDate)
      SELECT   @iMonthOfYear=DATEPART(month,   @dDate)
      SELECT   @sQuarter   =   'Q '   +     CAST(DATENAME   (quarter,   @dDate)as   varchar(1))

      INSERT   INTO   time_dimension(the_date,   the_day,   the_month,   the_year,
      day_of_month,
      week_of_year,   month_of_year,   quarter)   VALUES
      (@dDate,   @WeekString,   @sMonth,   @iYear,   @iDayOfMonth,   @iWeekOfYear,
      @iMonthOfYear,   @sQuarter)
      SELECT   @dDate   =   @dDate   +   @adddays
END
GO