計算一個月內的條目數

Question

我有一個訂單表，它有一個名爲order_date的日期時間列。我想在2009年計算每個月的訂單數量。我該怎麼做？

Answer 1

select month(order_date) as orderMonth, count(*) as orderCount 
from order 
where year(order_date) = 2009 
group by month(order_date) 
order by month(order_date) 

爲了參考，見在Transact-SQL month和year命令。

Answer 2

SELECT MONTH(order_date) AS ordermonth, 
    COUNT(*) AS ordercount 
FROM order 
WHERE YEAR(order_date) = 2009 
GROUP BY ordermonth; 

Answer 3

如何使用一些整潔的DATETIME技巧？

select 
    DATEADD(MONTH, DATEDIFF(MONTH, 0, order_date), 0) AS orderMonth, count(*) as orderCount 
from 
    [order] 
where 
    order_date >= '2009-01-01' 
group by 
    DATEADD(MONTH, DATEDIFF(MONTH, 0, order_date), 0) 
order by 
    orderMonth