SQL calculating percentage of sum

Question

I've got this tables:

Now I want to get the percentage of hours spent on projects which employees of 'XYZ GmbH' worked on.

So I need to get the complete spent hours by:

SELECT SUM(STDANZ)
  FROM MITPRO;

...and the hours spent by XYZ-GmbH on their projects by:

SELECT SUM(mp.STDANZ)
  FROM PROJEKT p INNER JOIN MITPRO mp ON (p.PNR = mp.PNR)
                 INNER JOIN FIRMA f ON (f.FNR = p.FNR)
 WHERE f.FNAME='XYZ GmbH';

The formula would then be:

 SUM(STDANZ_of_XYZ) / SUM(TOTAL) * 100

I tried this, but I always get an error:

SELECT SUM(mp.STDANZ) / (SELECT SUM(STDANZ) FROM MITPRO)
  FROM PROJEKT p INNER JOIN MITPRO mp ON (p.PNR = mp.PNR)
                 INNER JOIN FIRMA f ON (f.FNR = p.FNR)
 WHERE f.FNAME='XYZ GmbH';

The error says that it's not a single-group group function.

What should I do?

Thanks, Julian

Answer 1

SELECT AA.FSUM/BB.TSUM FROM
(
    SELECT SUM(mp.STDANZ)  AS FSUM
    FROM PROJEKT p INNER JOIN MITPRO mp ON (p.PNR = mp.PNR)
                     INNER JOIN FIRMA f ON (f.FNR = p.FNR)
    WHERE f.FNAME='XYZ GmbH'
) AA ,
(
    SELECT SUM(STDANZ) AS TSUM FROM MITPRO
)BB

Here AA and BB are intermediate temp tables which contain single sum row each. We are doing a CROSS JOIN on these 2 single row tables which essentially gives a single row.

Answer 2

You want to get the percentage of hours spent on projects which employees of 'XYZ GmbH' worked on (which means for each employee and not for all employees together), here's one way of doing it, there are 2 steps to this:

1. Get the total hours for the 'xyz..' project : For this part you had given the query as sum(all values), which i believe is not right as we must take the total hours for the entire project specific to 'xyz' and arrive at the percentage by computing the hours for the 'people' who had worked for it. However, if my assumption is incorrect, please change the first query below to get the total sum, rest should be fine.
2. Get the total hours for each employee and arrive at the percentage

See below query:

--1. Identify the total hours for the project itself (so as to arrive at the percentage); from your question, 
-- we need to consider only xyz gmbh project
DECLARE @TOTAL_SUM INT

SET @TOTAL_SUM = 
(SELECT
    SUM(MI.STDANZ) TOTAL_SUM 
FROM
    FIRMA F
    INNER JOIN PROJEKT P
    ON F.FNR = P.FNR
    INNER JOIN MITPRO MI
    ON MI.PNR = P.PNR
    --INNER JOIN MITARBEITER M
    --ON M.MNR = MI.MNR
WHERE
    F.FNAME = 'XYZ GmbH')t


--2. Identify the total hours for each employee for the xyz gmbh project
SELECT
    M.MNR   -- Employee id
    ,M.MName -- Employee name
    ,SUM(MI.STDANZ) TOTAL_SUM -- Total hours
    , (SUM(MI.STDANZ) / @TOTAL_SUM)*100 AS PERCENTAGE --Percentage of hours
FROM
    FIRMA F
    INNER JOIN PROJEKT P
    ON F.FNR = P.FNR
    INNER JOIN MITPRO MI
    ON MI.PNR = P.PNR
    INNER JOIN MITARBEITER M
    ON M.MNR = MI.MNR
WHERE
    F.FNAME = 'XYZ GmbH'
GROUP BY
    M.MNR
    ,M.MNAME