Home/ Questions/Q 4048810
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-20T13:51:53+00:00

I am writing a query against an advanced many-to-many table in my database. I

  • 0

I am writing a query against an advanced many-to-many table in my database. I call it an advanced table because it is a many-to-many table with and extra field. The table maps data between the fields table and the students table. The fields table holds potential fields that a student can used, kind of like a contact system (i.e. name, school, address, etc). The studentvalues table that I need to query against holds the field id, student id, and the field answer (i.e. studentid=1; fieldid=2; response=Dave Long).

So my table looks like this:

Table Layout

What I need to do is take a few passed in values and create a grouped accumulated report. I would like to do as much in the SQL as possible.

So that data that I have will be the group by field (a field id), the cumulative field (a field id) and I need to group the students by the group by field and then in each group count the amount of students in the cumulative fields.

So for example I have this data

ID     STUDENTID     FIELDID     RESPONSE 
1      1             2 *(city)*  Wallingford
2      1             3 *(state)* CT
3      2             2 *(city)*  Wallingford
4      2             3 *(state)* CT
5      3             2 *(city)*  Berlin
6      3             3 *(state)* CT
7      4             2 *(city)*  Costa Mesa
8      4             3 *(state)* CA

I am hoping to write one query that I can generate a report that looks like this:

CA - 1 Student
Costa Mesa          1

CT - 3 Students
Berlin              1
Wallingford         2

Is this possible to do with a single SQL statement or do I have to get all the groups and then loop over them?

EDIT Here is the code that I have gotten so far, but it doesn’t give the proper stateSubtotal (the stateSubtotal is the same as the citySubtotal)

SELECT state, count(state) AS stateSubtotal, city, count(city) AS citySubtotal
FROM(
  SELECT s1.response AS city, s2.response AS state
  FROM studentvalues s1
  INNER JOIN studentvalues s2
    ON s1.studentid = s2.studentid
  WHERE s1.fieldid = 5
    AND s2.fieldid = 6
) t
GROUP BY city, state
Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    So to make a table that looks like that, I would assume something like

    State  StateSubtotal   City         CitySubtotal
CA     1               Costa Mesa   1
CT     3               Berlin       1
CT     3               Wallingford  2

    Would be what you want. We can’t just group on Response, since if you had a student answer LA for city, and another student that responds LA for state (Louisiana) they would add. Also, if the same city is in different states, we need to first lay out the association between a city and a state by joining on the student id.

    edit – indeed, flawed first approach. The different aggregates need different groupings, so really, one select per aggregation is required. This gives the right result but it’s ugly and I bet it could be improved on. If you were on SQL Server I would think a CTE would help but that’s not an option. 

    select t2.stateAbb, stateSubtotal, t2.city, t2.citySubtotal from 
(
select city, count(city) as citySubTotal, stateAbb from (
select s1.Response as city, s2.Response as StateAbb
from aaa s1 inner join aaa s2 on s1.studentId = s2.studentId 
where s1.fieldId = 2 and s2.fieldId=3
) t1 
group by city, stateabb
) t2 inner join (
select stateAbb, count(stateabb) as stateSubTotal from (
select s1.Response as city, s2.Response as StateAbb
from aaa s1 inner join aaa s2 on s1.studentId = s2.studentId 
where s1.fieldId = 2 and s2.fieldId=3
) t3 
group by stateabb
) t4 on t2.stateabb = t4.stateabb
    • 0