Question

I am using Windows 7, Access 2010

I have a database that I need to return a random set of records from. The tables are relational.

I have the following tables:

• Competencies
• Elements
• Sections
• Examples

I created a query with an expression that numbered the records and I was able to randomly select x number of records.

The issue is:
Within the Elements, I need to RANDOMLY select x number of Sections within EACH element. So with my current set up I get x number of sections but it does not include at least one section from each Element. I would like to return say 25% of sections from each element.

i.e.
Element: 7.1, 7.2, 7.3, 7.4
Section: 7.1.1, 7.1.2, 7.1.3: 7.2.1, 7.2.2, 7.3.3 etc

My query is returning randomly but not from EACH element. So I might have all from element 7.1, 1 from 7.2 and nothing from 7.3 or 7.4.

Is there a way to do this? I think I might need a loop but I am completely unfamiliar with that so I’d need help with the appropriate VBA code to get it to work.

I have googled everything I can think of and I’m not getting anywhere.

Any help would be greatly appreciated!

Thank you.

Answer 1

You should be able to use a “select n from group” type of query, but you will need a unique ID:

SELECT
  t.ID, 
  t.Element, 
  t.Section
FROM Elements AS t
WHERE t.ID In (
     SELECT Top 2 ID 
     FROM Elements q 
     WHERE q.Element=t.Element 
     ORDER BY Rnd([id])*1000)

I have been over this a number of times and I reckon you are going to have to add a field for your random sort, then update the field before you run the query. This will update a field called RandomNumber in [Competency Elements]

 UPDATE [Competency Elements] 
 SET [Competency Elements].RandomNumber = Rnd([element id])*1000;

Then the percentage select, I think it has to be greater than 33 for this particular data set:

SELECT Val([comp section number]) AS [Sect No],
       s.[section description],
       e.[element number],
       e.[element description],
       Rnd(e.[element id])        AS Expr1,
       s.[section id],
       e.[element id],
       x.example,
       s.[competency id],
       c.[comp number],
       c.[competency category]
FROM   competencies AS c
       INNER JOIN (([competency sections] AS s
                    INNER JOIN [competency elements] AS e
                            ON s.[section id] = e.[section id])
                   INNER JOIN examples AS x
                           ON e.[element id] = x.[element id])
               ON c.[competency id] = s.[competency id]
WHERE  (( ( e.[element id] ) IN (SELECT TOP 35 PERCENT [element id]
                                 FROM   [competency elements] q
                                 WHERE  q.[section id] = e.[section id]
                                 ORDER  BY randomnumber) ))
ORDER  BY Val([comp section number]); 

There are a number of issues around getting a random selection from a group.