SQL Divide values by a total sum, groupwise - sql-server

Question

I have a table like:
user_id operation amount
1 purchase 10
1 sale 40
2 purchase 100
2 sale 20
2 conversion 15
3 sale 70
4 conversion 40
given by the SQL query:
SELECT
user_id,
operation,
COUNT(item_num) AS amount
FROM MyTable
GROUP BY user_id, operation
I want to calculate, for each user, the percentage of the total amount for each operation and it would be nice to place them in the columns(actually dividing numbers):
user_id purchase sale conversion
1 10 /50 40 /50 0 /50
2 100 /135 20 /135 15 /135
3 0 /70 70 /70 0 /70
4 0 /40 0 /40 40 /40
EDIT:
Thanks to the intuition given in the responses, I was able to find the solution that suits me best
WITH result
AS
(
SELECT
[user_id],
[operation],
CAST(COUNT([item_num]) AS float) AS amount,
SUM(COUNT([item_num])) over(partition by [user_id]) AS total_amount
FROM Mytable
GROUP BY user_id, operation
)
SELECT
[user_id],
ROUND(ISNULL([purchase], 0) / total_amount, 2) AS purchase,
ROUND(ISNULL([sale], 0) / total_amount, 2) AS sale,
ROUND(ISNULL([conversion], 0) / total_amount, 2) AS conversion
FROM result
PIVOT
(
MAX(amount)
FOR operation IN ([purchase], [sale], [conversion])
) x
ORDER BY user_id

Answer 1

This code will work for you. You will need to use a CTE with the columns and a sum() over() calculating the total sum per user_id.
With that information, all you need to do is pivot the result and give the formatting desired. If you need the division and not just showing what its dividing, remove the formating and concatenation.
WITH Sum_Over AS
(
select user_id,operation, amount,sum(amount) over(partition by user_id) AS Total_Sum
from #test
)
SELECT user_id
,CAST(ISNULL([purchase],0) AS VARCHAR(5))+'/'+CAST(Total_Sum AS VARCHAR(5)) AS [purchase]
,CAST(ISNULL([sale],0) AS VARCHAR(5))+'/'+CAST(Total_Sum AS VARCHAR(5)) AS [sale]
,CAST(ISNULL([conversion],0) AS VARCHAR(5))+'/'+CAST(Total_Sum AS VARCHAR(5)) AS [conversion]
FROM Sum_Over
PIVOT (
max(amount)
FOR operation IN ([purchase],[sale],[conversion])
)x
ORDER BY user_id

Answer 2

The answer from Jader is cleaner. This one uses Group By:
With result As
(
SELECT
user_id,
Sum(amount) as tot,
Case When operation = 'purchase' Then
convert(nvarchar(5),sum(amount)) + '/' + convert(nVarChar(50),(Select sum(amount) From MyTable t Where t.user_id = x.user_id))
End As [purchase],
Case When operation = 'sale' Then
convert(nvarchar(5),sum(amount)) + '/' + convert(nVarChar(50),(Select sum(amount) From MyTable t Where t.user_id = x.user_id))
End As [sale],
Case When operation = 'conversion' Then
convert(nvarchar(5),sum(amount)) + '/' + convert(nVarChar(50),(Select sum(amount) From MyTable t Where t.user_id = x.user_id))
End As [conversion]
FROM MyTable x
GROUP BY user_id, operation
)
Select user_id,
isnull(Max(purchase),'0/' + convert(nVarChar(50),sum(tot))) As purchase,
isnull(Max(sale),'0/' + convert(nVarChar(50),sum(tot))) As sale,
isnull(Max(conversion),'0/' + convert(nVarChar(50),sum(tot))) As conversion
From result
Group By user_id