Calculate Percentages In Query - Access SQL

问题

I'm trying to quantify some things. Here's a sample (simplified of course):

tblParent: { Number, Name }
tblChild: { Number, Name, ParentNumber, Criterion }

I'd like to count the total number of Children with the same ParentNumber (easy using a Group By and a Count(1) ), but the problem is comparing that number with the number of children with the same ParentNumber who have Criterion = "Something".

Here's what I have so far:

SELECT "Criterion = 1" AS CritDesc,
COUNT(1) AS Total,
ParentNumber AS Parent,
( COUNT(1) / (SELECT Total FROM [TotalCountingQuery]) ) AS Percentage
FROM tblChild
WHERE Criterion = 1
GROUP BY ParentNumber;

[TotalCountingQuery] simply counts all Children with each ParentNumber and puts that total into Total

SELECT COUNT(1) AS Total FROM tblChild GROUP BY ParentNumber;

So I'm trying to use that TOTAL count and figure out how many (as a percentage) have Criterion=1. But since it is using a subquery, the subquery cannot return more than one Total. I need it to return the total for each ParentNumber, to be used in the Percentage calc for each Child having that ParentNumber.

End result should be:

CritDesc   |    Total    |   Parent    |   Percentage
```````````````````````````````````````````````````````
Criterion=1|      2      |   45011     |      0.333    // Means there should be 6 Children with 45011 as parent
Criterion=1|      4      |   43255     |       0.9
Criterion=1|      1      |   59056     |      0.44

I have several of these queries which I union in a report to produce a full report, grouped by Parent, showing all "Criterion=X" for all Parents. That's working, I just need the above working.

Ideas?

EDIT: My attempt at a join for this purpose:

SELECT "Criterion=1" AS CritDesc,
COUNT(c.Number) AS Total,
ParentNumber AS Parent,
COUNT(c.Number)/q.Total AS Percentage
FROM tblChild AS c INNER JOIN tblParent AS q ON c.ParentNumber = q.Number
GROUP BY ParentNumber

This throws: You tried to execute a query ... 'Count(1)/q.Total' as part of an aggregate function. Adding it to the group-by statement throws Cannot have aggregate function in GROUP BY...

回答1:

Your subquery has no where clause and thus counts all records, but you can do it without subquery

SELECT
    "Criterion = 1" AS CritDesc,
    SUM(IIf(Criterion = 1, 1, 0)) AS NumCrit,
    COUNT(*) AS TotalNum,
    SUM(IIf(Criterion = 1, 1, 0)) / COUNT(*) AS Percentage,
    ParentNumber AS Parent
FROM
    tblChild
GROUP BY
    ParentNumber;

Note: I dropped the WHERE-clause. Instead I am counting the records fulfilling the criterion by summing up 1 for Criterion = 1 and 0 otherwise. This allows me to get the total number per ParentNumber at the same time with Count(*).

UPDATE

You might want to get results for parents having no children as well. In that case you can use an outer join

SELECT
    "Criterion = 1" AS CritDesc,
    SUM(IIf(C.Criterion = 1, 1, 0)) AS NumCrit,
    COUNT(C.Number) AS TotalNumOfChildren,
    SUM(IIf(C.Criterion = 1, 1, 0)) / COUNT(*) AS Percentage,
    P.Number AS Parent
FROM
    tblChild AS C
    LEFT JOIN tblParent AS P
        ON C.ParentNumber = P.Number  
GROUP BY
    P.Number;

Note that I get the total number of children with Count(C.Number) as Count(*) would count records with no children as well and yield 1 in that case. In the percentage calculation, however, I divide by Count(*) in order to avoid a division by zero. The result will still be correct in that case, since the sum of records with Criterion = 1 will be zero.

回答2:

If you are working within MS Access, you can divide by a DCount of parents.

Total/DCount("Parent","Table","Parent=" & Parent)

You could also create a count query

SELECT Parent, Count(Parent) FROM Table GROUP BY Parent

And then add both queries to the design grid joining them on Parent.

来源：https://stackoverflow.com/questions/11329936/calculate-percentages-in-query-access-sql

标签

sql

ms-access

group-by

percentage