sql-server - 如何在间隔内从 SQL Server 数据库返回值

Question

嗨，我有一个包含 3 列的 SQL 服务器数据库，Activity[start_date(datetime),end_date(datetime),title(string)] 我希望计算一整年，每个月有多少活动有 start_date，我的意思是我希望返回 12 个值（12 个月）来计算月份内的活动， 谢谢。

Answer 1

select month(start_date) as Month, count(*) as Count
from Activity
where year(start_date) = 2011 
group by month(start_date)
order by month(start_date)

Answer 2

如果有一个索引start_date和/或如果您需要在结果中包含月份，即使该月份没有活动，您也可以考虑这个：

DECLARE @year INT;
SET @year = 2012;

;WITH n AS 
(
  SELECT TOP (12) m = DATEADD(MONTH, ROW_NUMBER() OVER 
    (ORDER BY name)-1, DATEADD(YEAR, @year-1900, 0))
    FROM sys.all_objects ORDER BY name
)
SELECT [Month] = n.m, ActivityCount = COUNT(t.title) 
FROM n 
LEFT OUTER JOIN dbo.unspecified_table_name AS t
  ON t.start_date >= n.m
  AND t.start_date < DATEADD(MONTH, 1, n.m)
GROUP BY n.m
ORDER BY [Month];

（如果您不希望在给定月份的活动为零时出现一行，则更LEFT OUTER改为INNER。）