Grouping joined lookup values in Access [duplicate] - sql

Question

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Combine values from related rows into a single concatenated string value
(1 answer)
Closed 8 years ago.
My database includes several lookup tables (shown as pulldown menus on the UI form).
For example,
customer_data - customer demographic info.
lookup_car - stores car descriptions (Pinto, Vega, Reliant Robin, Mustang, Corvette)
junction_car_customer - joins a customer with one or more cars
Customer Jeremy Clarkson (cust_id: 1) owns three cars. The dropdown for his record shows:
Pinto (car_id=100)
Reliant Robin (car_id=101)
Vega (car_id=102)
The junction_car_customer data looks like this:
cust_id car_id
1 100
1 101
1 102
I'm trying to return a row showing the customer name and the models owned (as a semi-colon delimited string).
Here's my query:
SELECT
cd.cust_id,
cd.name_first,
cd.name_last,
jcc.car_id,
lc.car_desc
FROM
((customer_data AS cd)
LEFT JOIN ju_cust_car AS jcc ON jcc.cust_id = cd.cust_id)
LEFT JOIN lookup_cars AS lc ON lc.car_id = jcc.car_id
ORDER BY
cd.name_last
This returns:
cust_id name_first name_last car_id car_desc
1 Jeremy Clarkson 100 Pinto
1 Jeremy Clarkson 101 Reliant Robin
1 Jeremy Clarkson 102 Vega
What I'd like is:
cust_id name_first name_last car_desc
1 Jeremy Clarkson Pinto;Reliant Robin;Vega
Is there an efficient way of returning the above result?

Answer 1

As HansUp says, you need to use a custom VBA function. If the data is fairly static, you can speed things up by caching the results. So...
1) In the VB editor, add a reference to the 'Microsoft Scripting Runtime' (we'll be needing the Dictionary class from this library).
2) Create a new standard module, and add code to it like the following:
Option Explicit
Private mCache As New Scripting.Dictionary
Sub ClearCarDescCache(Optional cust_id)
If IsMissing(cust_id) Then
mCache.RemoveAll
Else
mCache.Remove CInt(cust_id)
End If
End Sub
Function GetCarDescList(cust_id) As String
If mCache.Exists(cust_id) Then
GetCarDescList = mCache(cust_id)
Exit Function
End If
Dim RS As DAO.Recordset, S As String
Set RS = CurrentDb.OpenRecordset( _
" SELECT car_desc " + _
" FROM junction_car_customer INNER JOIN lookup_car " + _
" ON junction_car_customer.car_id = lookup_car.car_id " + _
" WHERE cust_id = " & cust_id & _
" ORDER BY car_desc", dbOpenForwardOnly)
While Not RS.EOF
If Len(S) = 0 Then
S = RS(0)
Else
S = S + ";" & RS(0)
End If
RS.MoveNext
Wend
mCache.Add cust_id, S
GetCarDescList = S
End Function
3) The main query can now look like this:
SELECT cust_id, name_first, name_last, GetCarDescList(cust_id) AS car_desc
FROM customer_data
ORDER BY name_last
4) Add explicit calls to ClearCarDescCache as appropriate.