子查詢按月和年分組

Question

我有一個包含三列的表：

id (nvarchar)
time (datetime)
description (nvarchar)

並要計算以下數量：

SELECT 
(
(SELECT CAST(COUNT(DISTINCT id) as float)
FROM [table]
WHERE description = 'x'
) / 
(
(SELECT CAST(COUNT(DISTINCT id) as float)
FROM [table])
)
AS quotient

有沒有一種方法可以計算每個月和每年而不是整個表的相同商？ 我在最后嘗試了GROUP BY MONTH(time) + YEAR(time) ，但收到以下錯誤消息：

多部分標識符無法綁定。

Answer 1

嘗試這個：

SELECT YEAR(time), MONTH(time), 
       COUNT(DISTINCT CASE WHEN description = 'x' THEN id END)  /
       (COUNT(DISTINCT id) * 1.0) AS quotient
FROM [table]
GROUP BY YEAR(time), MONTH(time)