Percentage from Total SUM after GROUP BY SQL Server

Question

I have these results:

PersonID    SUM(PA.Total)
-------------------------
   1            75
   2            75
   3            15
   4            15
   5            60
   6            60

With the table like:

PersonID    Total
------------------
   1         50
   2         50
   3         10
   4         10
   5         40
   6         40
   1         25
   2         25
   3          5
   4          5
   5         20
   6         20

These are grouped by the person. Now I'm looking to add a column with the percentages for each person calculated from the total of all of their sums.

For example: the total sum is 300, and hence I need a result like this:

PersonID    SUM(PA.Total)   Percentage
--------------------------------------
   1            75              25%
   2            75              25%
   3            15              5%
   4            15              5%
   5            60              20%
   6            60              20%

I have looked at code online and I have come up with a fix such as this:

 SELECT 
     P.PersonID, SUM(PA.Total)
     SUM(PA.Total) * 100 / [p] AS 'Percentage'
 FROM 
     Person P
 JOIN 
     Package PA ON P.PersonID = PA.PackageFK
 CROSS JOIN 
     (SELECT SUM(PA.[Total]) AS [p] 
      FROM Package PA) t
 GROUP BY 
     P.PersonID

But I'm unsure how to incorporate the cross join into the join as well as the already group/sum section. Or whether this is along the right lines altogether.

Any help would be appreciated - SQL fiddle http://sqlfiddle.com/#!9/80f91/2

Answer 1

You don't need a cross join. Just use window functions:

SELECT P.PersonID, SUM(PA.Total),
       SUM(PA.Total) * 100.0 / SUM(SUM(PA.Total)) OVER () AS Percentage
FROM Person P JOIN
     Package PA
     ON P.PersonID = PA.PackageFK
GROUP BY P.PersonID;

Note that you do not need the JOIN for this query:

SELECT PA.PersonID, SUM(PA.Total),
       SUM(PA.Total) * 100.0 / SUM(SUM(PA.Total)) OVER () AS Percentage
FROM Package PA
GROUP BY PA.PersonID;

SQL Server does integer division. I do such calculations using decimal numbers so they make more sense.

Here is a SQL Fiddle, with two changes:

1. The database is changed to SQL Server.
2. The total is stored as a number rather than a string.