计算周数

Question

我有一个名为Calendar的表，数据看起来像：

Date                         Week_Num       Month_Year
1996-01-27 00:00:00.000      1021            01/1997
1996-01-28 00:00:00.000      1021            01/1997
1996-01-29 00:00:00.000      1021            01/1997
1996-02-03 00:00:00.000      1022            01/1997
1996-02-04 00:00:00.000      1022            01/1997
1996-02-10 00:00:00.000      1023            01/1997
1996-02-11 00:00:00.000      1023            01/1997

我想计算一个月内的周数：

我写了一个像：

这样的查询

Select Month_year,Count(*)
From (Select Week_Num,Month_year
      From Calendar
      Group By Week_Num,Month_year
      )a
Group By Month_year
order by Month_year

这给了我想要的东西但是有更好的方法吗？

Answer 1

SELECT Month_Year, COUNT(DISTINCT Week_Num)
FROM Calendar
GROUP BY Month_Year

这将删除一个级别的聚合，并且更具可读性。不过，我不确定它是否会有更好的表现。

证明概念的样本：

DECLARE @t table (DT smalldatetime, week_num int, month_year varchar(100))

INSERT INTO @t
VALUES
('1996-01-27 00:00:00.000', 1021,'01/1997'),
('1996-01-28 00:00:00.000', 1021,'01/1997'),
('1996-01-29 00:00:00.000', 1021,'01/1997'),
('1996-02-03 00:00:00.000', 1022,'01/1997'),
('1996-02-04 00:00:00.000', 1022,'01/1997'),
('1996-02-10 00:00:00.000', 1023,'01/1997'),
('1996-02-11 00:00:00.000', 1023,'01/1997')

SELECT Month_Year, COUNT(DISTINCT Week_Num)
FROM @t
GROUP BY Month_Year

<强>返回：

Month_Year  (No column name)
01/1997         3

Answer 2

我这就是你所需要的：

Select Month_year,Count(distinct Week_Num)
From Calendar
Group By Month_year
order by Month_year