My question is given a 1-Many relation ship where the children are stored on 1 ChildTable,
ChildID | ParentID | Data2 | InputDate
------------------------------------
1 | 345 | 100 | 3-5-2016
2 | 345 | 0 | 3-12-2016
3 | 345 | 150 | 3-19-2016
4 | 345 | 0 | 4-20-2016
... more children with different parent IDs
and also given that the parents are stored on their own ParentTable with ParentID... Data etc.
My question is how does one partition or update query a similar database so that if the data column has a value 0 then it updates with the last input data. (Say a web scraper failed to pull the data and I want to approximate for analysis). The raw data doesn't have to be updated on the base table, but also could be updated in a query pulling it. I believe there's a way using SQL to make this doable. My attempt was incredibly slow and didn't work for unknown reasons..
I've tried writing some VBA-Access code to loop through a flat file ChildTable + ParentTable and update every 0-value cell in the column Data using an SQL Lookup. If the cell = 0 then go to last available data that is nonzero. The problem si that this takes years to run.
Option Compare Database
Sub SoldOut()
On Error GoTo ProcError
Dim rs As DAO.Recordset
Set rs = CurrentDb.OpenRecordset("MainDataTable") 'This is the flat file version of the data above
'Check to see if the recordset actually contains rows
If Not (rs.EOF And rs.BOF) Then
rs.MoveLast
rs.MoveFirst 'Unnecessary in this case, but still a good habit
Do Until rs.EOF = True
GetLastWeek = 0
If Not rs("Data") > 0 Then
rs.Edit
rs("Data") = GetLastWeek(rs('ChildID'), rs('ParentID'), rs('Data'), rs('InputDate'))
rs.Update
End If
'Move to the next record. Don't ever forget to do this.
rs.MoveNext
Loop
Else
MsgBox "There are no records in the recordset."
End If
ProcExit:
On Error Resume Next
rs.Close 'Close the recordset
Set rs = Nothing 'Clean up
Exit Sub
ProcError:
MsgBox Err.Description
Resume ProcExit
End Sub
Private Function GetLastWeek(ChildID, ParentID As Long, InputDate As Date) As Integer
'given a record it looks up the weeks before and returns it if it exists
Dim rst As DAO.Recordset, strSQL As String, rc As Integer ' SQL Code for seeing if last week's data exists.
strSQL = "SELECT * " & _
"FROM MainDataTable " & _
"WHERE MainDataTable.[ParentId] = " & ParentID & "AND MainDataTable.[InputDate] <# " & InputDate & "AND NOT MainDataTable.[Data] = 0
ORDER BY MainDataTable.[InputDate] DESC;"
Set rst = CurrentDb.OpenRecordset(strSQL): rst.MoveLast: rst.MoveFirst
rc = rst.RecordCount
If rc = 0 Then GoTo Cleanup 'if no record, then we are out of luck
If rc > 0 Then 'If there's some Record
Do Until rs.EOF = True Or GetLastWeek > 0
Dim price As Integer: price = rst("Data")
If price > 0 Then: GetLastWeek = price
rs.MoveNext
Loop
End If
Cleanup:
rst.Close
Set rst = Nothing
If GetLastWeek = 0 Then GetLastWeek = 1 '1 means no data was found
'Set so the output if nothing is found to 1 so that the code doesn't have to run on the same rows every single week
End Function
I'm not sure how what you have can work, but all you should have to do is iterate through your main table ordered by parentid, date asc
and then save the parentID and data value for use in the next iteration ( Dim lDataValPrev as long
) as long as it's non-zero. If the current data value is zero and the parentID hasn't changed, replace it with the previous value you stored. You should only have to go through your data once with no additional calls.
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.