Question

我有一个表a，其中包含a.A，a.B和a.C。

我正在尝试通过查询使字段b.A，b.B，b.C，b.D成为表b：

SELECT a.A, a.B, a.C, 
(Sequential integers from first record returned to last record returned) AS D 
into b
FROM a WHERE a.C is not null
ORDER BY a.C, a.B DESC, a.A;

表b的示例输出：

A, B, C, D
9500, 106.12, 9507, 1
9507, 106.12, 9516, 2
9485, 106.11, 9516, 3
9472, 106.1, 9516, 4
9432, 106.09, 9516, 5
9528, 106.14, 9531, 6
9523, 106.13, 9536, 7
9531, 106.14, 9540, 8
9540, 106.14, 9545, 9
9545, 106.14, 9548, 10
9548, 106.14, 9555, 11
9570, 106.21, 9572, 12
9575, 106.22, 9580, 13
9580, 106.22, 9583, 14

A是唯一标识符。

这将在具有数百万条记录的表上运行。

我的挑战是（从返回的第一条记录到返回的最后一条记录的顺序升序整数）。有人对括号中的内容有什么建议，这将有助于我仅使用查询创建表b？

Answer 1

我认为最简单的方法是先定义新表并使用insert：

create table b (
    b_id autoincrement primary key,
    a ?,  -- ? is for the type of the column
    b ?,
    c ?
);

insert into b (a, b, c)
    select a.A, a.B, a.C, 
    from a 
    where a.C is not null
    orer by a.C, a.B desc, a.A;

MS Access没有方便的功能，例如row_number()（几乎所有其他数据库都支持）来简化此操作。

Answer 2

您可以使用我的函数 RowNumber ：

' Builds consecutive row numbers in a select, append, or create query
' with the option of a initial automatic reset.
' Optionally, a grouping key can be passed to reset the row count
' for every group key.
'
' 2018-08-23. Gustav Brock, Cactus Data ApS, CPH.
'
Public Function RowNumber( _
    ByVal Key As String, _
    Optional ByVal GroupKey As String, _
    Optional ByVal Reset As Boolean) _
    As Long

    ' Uncommon character string to assemble GroupKey and Key as a compound key.
    Const KeySeparator      As String = "¤§¤"
    ' Expected error codes to accept.
    Const CannotAddKey      As Long = 457
    Const CannotRemoveKey   As Long = 5

    Static Keys             As New Collection
    Static GroupKeys        As New Collection
    Dim Count               As Long
    Dim CompoundKey         As String

    On Error GoTo Err_RowNumber

    If Reset = True Then
        ' Erase the collection of keys and group key counts.
        Set Keys = Nothing
        Set GroupKeys = Nothing
    Else
        ' Create a compound key to uniquely identify GroupKey and its Key.
        ' Note: If GroupKey is not used, only one element will be added.
        CompoundKey = GroupKey & KeySeparator & Key
        Count = Keys(CompoundKey)

        If Count = 0 Then
            ' This record has not been enumerated.
            '
            ' Will either fail if the group key is new, leaving Count as zero,
            ' or retrieve the count of already enumerated records with this group key.
            Count = GroupKeys(GroupKey) + 1
            If Count > 0 Then
                ' The group key has been recorded.
                ' Remove it to allow it to be recreated holding the new count.
                GroupKeys.Remove (GroupKey)
            Else
                ' This record is the first having this group key.
                ' Thus, the count is 1.
                Count = 1
            End If
            ' (Re)create the group key item with the value of the count of keys.
            GroupKeys.Add Count, GroupKey
        End If
        ' Add the key and its enumeration.
        ' This will be:
        '   Using no group key: Relative to the full recordset.
        '   Using a group key:  Relative to the group key.
        ' Will fail if the key already has been created.
        Keys.Add Count, CompoundKey
    End If

    ' Return the key value as this is the row counter.
    RowNumber = Count

Exit_RowNumber:
    Exit Function

Err_RowNumber:
    Select Case Err
        Case CannotAddKey
            ' Key is present, thus cannot be added again.
            Resume Next
        Case CannotRemoveKey
            ' GroupKey is not present, thus cannot be removed.
            Resume Next
        Case Else
            ' Some other error. Ignore.
            Resume Exit_RowNumber
    End Select

End Function

和类似于以下内容的附加查询：

INSERT INTO TempTable ( [RowID] )
SELECT RowNumber(CStr([ID])) AS RowID, *
FROM SomeTable
WHERE (RowNumber("","",True)=0);

包括演示的完整说明可以在这里找到：

Sequential Rows in Microsoft Access

以及在GitHub上：VBA.RowNumbers

在按三个字段排序的表上添加顺序索引

2 个答案: