MS Access/Access-SQL: Switch Function to Calculate Distances based on Criteria - sql

Question

I am somewhat new to MS Access/SQL and StackOverflow, so bear with me. I have a problem that I can't seem to figure out. I had posted this before, but got no responses, and editing my original post did not help.
I have quantity and distance data for assets for each week. Not all weeks have Quantity or distances (some just have 1 or the other). Here is a sample of the data for one asset(put in CSV):
Asset,Week,Qty,Dist,Actual_Dist
2153,1,,125,
2153,2,,65,
2153,3,50.1,118,
2153,4,,123,
2153,5,96.6,91,
2153,6,,103,
2153,7,,120,
2153,8,,106,
2153,9,100.6,,
2153,13,96,,
2153,14,,102,
2153,15,,40,
2153,18,84.82,,
2153,21,97.8,,
2153,25,96.7,,
2153,28,31.27,63,
2153,29,77.5,,
What I want to be able to do, is take a SUM of the "DIST" field until the row has a corresponding "QTY" field value, and this would be calculated in the "Actual_Dist" field.
Looking at my example, Weeks 1 and 2 have no Qty values, however in Week 3, Qty is 50.1 and I would want the "Actual_Dist" calculated as the sum of "Dist" from Weeks 1-3 inclusive. So essentially, Row 3's "Actual_Dist" would be SUM(125+65+118).
Right now I see 3 cases:
Case 1: as above, if no Qty, but has a Dist, then sum the distances until the next Qty value.
Case 2: If Qty exists, but no Dist, then disregard
Case 3: If Qty has a value, and Dist has a value, and Qty has previous values before (ie., Week 28), then "Actual_Dist" = Dist
So I was thinking of doing a select switch to cover the two main cases (1 & 3):
Select Asset, Week, Qty, Dist, Switch (Qty like 'NULL' AND Dist <> 'NULL', SUM(Dist) AS Actual_Dist, Switch (Qty <> 'NULL AND Dist <> 'NULL', DIST) AS Actual_Dist
**Not sure if my Switch is done right, but I think you get the picture?
Now my issues comes in the sum function above. How do I get it sum properly and take the distance values before a qty value is present (Case 2)? I apologize if the formatting or presentation of sample data is poor. Just signed up. I will likely have to clarify some points, so let me know and I will clarify as necessary.
It is also important to note that this is just one asset, and there are many. For the sum function above, I need it to be able to sum the records above for ANY given number of records.
Hope someone can help.
Thanks
EDIT: #Cha had posted the following:
SELECT Data.Asset, Data.Week, Data.Qty, Data.Dist, Switch(Not IsNull([Qty]) And Not IsNull([Dist]),[Dist], Not IsNull([Qty]),Nz(DSum("Dist","Data","Asset=" & CStr([Asset]) & " And Week <= " & CStr([Week]) & " And Week > " & CStr(Nz(DMin("Week","Data","Asset=" & CStr([Asset]) & " And Week < " & CStr([Week]) & " And Not IsNULL(Qty)"),0))),0)) AS Actual_Dist FROM Data;
This code gave me errors due to data mismatch, so I changed all the data types to "Number" and modified the code as follows:
SELECT Data.Asset, Data.Week, Data.Qty, Data.Dist, Switch(Not IsNull([Qty]),Nz(DSum("Dist","[Data]","Asset=" & [Asset] & " And Week <= " & [Week] & " And Week > " & Nz(DMin("Week","[Data]","Asset=" & [Asset] & " And Week < " & [Week] & " And Not IsNULL([Qty])"),0)),0)) AS Actual_Dist
FROM Data;
The above code now satisfies Case 1, but only satisfies it for Row 3 and 5. This Case does not satisfy Rows 9 and 13, and it needs to apply there too. I believe the issue with those rows is that the "Dist" is NULL.
There is another issue, Case 1 and Case 3 overwrite eachother occasionally (when both Qty and Dist are not NULL. Is there a way to create 1 switch to run Case 1, and another (with the same code) to apply Case 3 but not Case 1?
Any help would be much appreciated!
Thanks

Answer 1

If you can use VBA, then try this:
Public Sub GetActual_Dist()
Const TABLE_NAME As String = "tblAssets"
Dim sTemp_Dist As Single
With CurrentDb.OpenRecordset("SELECT * FROM [tblAssets] WHERE NOT ([Qty] is not Null AND [Dist] is Null);")
If .EOF And .BOF Then
MsgBox "No data"
Exit Sub
End If
Do Until .EOF
If ![Qty] Is Null Then
sTemp_Dist = sTemp_Dist + ![Dist]
Else
.Edit
![Actual_Dist] = sTemp_Dist
.Update
sTemp_Dist = 0
End If
.MoveNext
Loop
End With
End Sub
Change the TABLE_NAME to the one in your database.