计数不同？

Question

我有一张“购买”表：

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

我正在尝试计算每个月和每年购买的客户数量。 我该怎么做？

Answer 1

只要您不需要包括没有购买的月份：

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 SQL 系统，但在某些系统上不受支持（如 MS Access）。

Answer 2

每年的客户购买量

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

客户按月购买

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

Answer 3

您可以使用 group by 的常见查询来实现您想要的结果。

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