访问 SQL：根据条件更新一对多关系中的 Children

Question

我的问题是一个一对多关系，其中 children 存储在 1 个 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

并且考虑到 parents 存储在它们自己的带有 ParentID 的 ParentTable 中...数据等

我的问题是分区或更新如何查询类似的数据库，以便如果数据列的值为 0，则它会更新为最后的输入数据。（假设网络抓取工具无法提取数据，我想进行近似分析）。原始数据不必在基础 table 上更新，但也可以在拉取它的查询中更新。我相信有一种方法可以使用 SQL 来实现。我的尝试非常慢，而且由于未知原因没有成功..

我尝试编写一些 VBA-Access 代码来遍历平面文件 ChildTable + ParentTable 并使用 SQL 查找更新数据列中的每个 0 值单元格。如果单元格 = 0，则转到非零的最后可用数据。问题是这需要数年时间才能运行.

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

Answer 1

我不确定你所拥有的是如何工作的，但你所要做的就是遍历 parentid, date asc 订购的主 table，然后保存 parentID 和数据值只要它不为零，就会在下一次迭代 (Dim lDataValPrev as long) 中使用。如果当前数据值为零且 parentID 未更改，请将其替换为您存储的先前值。您只需检查一次数据，无需额外调用。

访问 SQL：根据条件更新一对多关系中的 Children

Access SQL: Updating Children in a 1 to Many relationship based on criteria

sql

ms-access

vba

one-to-many