算不同？

Question

我有一张桌子＆＃34;购买＆＃34;：

CustomerId . PurchaseYear . PurchaseMonth
1234       . 2012         . 6 
1235       . 2012         . 7
1236       . 2013         . 4
1237       . 2015         . 6
1238       . 2015         . 6

我试图计算每个月和每年购买的客户数量。我该怎么做呢？

Answer 1

只要您不需要包含没有购买的月份：

SELECT PurchaseYear, PurchaseMonth, COUNT(DISTINCT CustomerId)
FROM {table}
GROUP BY PurchaseYear, PurchaseMonth

请注意COUNT(DISTINCT xxx)适用于所有主要的SQL系统，但某些（例如MS Access）不支持。

Answer 2

按年度购买客户

Select PurchaseYear, Count(DISTINCT CustomerId) As CustomerPurchases
FROM Purchases
GROUP BY PurchaseYear

按月购买客户

Select PurchaseYear, PurchaseMonth, Count(DISTINCT CustomerId) As CustomerPurchases
FROM Purchases
GROUP BY PurchaseYear, PurchaseMonth

Answer 3

您的愿望结果可以使用分组的常见查询来实现。

Select PurchaseYear , PurchaseMonth, Count(CustomerId) as TotalCustomer, 
From Purchase 
Group by PurchaseYear, PurchaseMonth