頻率分佈與加權平均

Question

我有以下格式的數據：

TYPE AMOUNT 
Book £2 
Pen £1 
Book £3 

我試圖輸出這是一個加權平均值：

TYPE Weighted Average 
Book 0.833333333 
Pen 0.166666667 

到目前爲止，我有：

Select TYPE, AMOUNT/SUM(AMOUNT) 
FROM MyTable 
Group by TYPE 

Answer 1

這應該會給你想要的結果：

select type 
    , cast(sum(amount) as decimal(10,5))/(select sum(amount) from t) 
from t 
group by type 

見Sql Fiddle for Demo

Answer 2

這將工作

DECLARE @Table1 TABLE (TYPE VARCHAR(10),AMOUNT FLOAT) 
INSERT INTO @Table1 SELECT 'Book',2 UNION ALL SELECT 'Pen',1 UNION ALL SELECT 'Book',3 

DECLARE @Total FLOAT 
SELECT @Total=SUM(AMOUNT) FROM @Table1 

SELECT TYPE,SUM(AMOUNT/@Total) FROM @Table1 GROUP BY TYPE