sql server中統計多個互斥數據的數量

建立表

CREATE TABLE [dbo].[color](
	[id] [int] IDENTITY(1,1) NOT NULL,
	[color] [varchar](50) NULL
) ON [PRIMARY]

 隨機插入數據 

id	color
1	green
2	red
3	blue
4	green
5	red
6	red

統計每種 顏色的數量

當須要使用一個語句查詢每種顏色的數量時，不能把顏色條件放進WHERE條件中, 由於每種顏色是互斥的。

red	blue	green
3	1	2

下面SQL可獲得上面的結果：

SELECT
    SUM(CASE WHEN(color = 'red') THEN 1 END) AS red,
    SUM(CASE WHEN(color = 'blue') THEN 1 END) AS blue,
    SUM(CASE WHEN(color = 'green') THEN 1 END) AS green
  FROM [dbo].[color]

或者

SELECT
    COUNT(CASE WHEN(color = 'red') THEN 1 END) AS red,
    COUNT(CASE WHEN(color = 'blue') THEN 1 END) AS blue,
    COUNT(CASE WHEN(color = 'green') THEN 1 END) AS green
  FROM [dbo].[color]