循环访问 MS Access 中所有记录的代码

Posted 2023-04-19

【中文标题】循环访问 MS Access 中所有记录的代码

【英文标题】：Code to loop through all records in MS Access

【发布时间】：2011-05-03 01:27:06

【问题描述】：

我需要一个代码来循环遍历表中的所有记录，以便提取一些数据。除此之外，是否还可以遍历过滤记录​​并再次提取数据？谢谢！

【参考方案1】：

您应该能够使用非常标准的 DAO 记录集循环来执行此操作。您可以在以下链接中查看一些示例：http://msdn.microsoft.com/en-us/library/bb243789%28v=office.12%29.aspxhttp://www.granite.ab.ca/access/email/recordsetloop.htm

我自己的标准循环如下所示：

Dim rs As DAO.Recordset
Set rs = CurrentDb.OpenRecordset("SELECT * FROM Contacts")

'Check to see if the recordset actually contains rows
If Not (rs.EOF And rs.BOF) Then
    rs.MoveFirst 'Unnecessary in this case, but still a good habit
    Do Until rs.EOF = True
        'Perform an edit
        rs.Edit
        rs!VendorYN = True
        rs("VendorYN") = True 'The other way to refer to a field
        rs.Update

        'Save contact name into a variable
        sContactName = rs!FirstName & " " & rs!LastName

        '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

MsgBox "Finished looping through records."

rs.Close 'Close the recordset
Set rs = Nothing 'Clean up

【讨论】：

仅供参考，您应该将您的rs.Close 封装为If Not rs = Nothing Then Set rs.Close。如果由于某种原因，您的 Set 语句失败，您的代码将在此处出错。我的 0.02c。

【参考方案2】：

在“引用”中，导入 DAO 3.6 对象引用。

private sub showTableData

dim db as dao.database
dim rs as dao.recordset

set db = currentDb
set rs = db.OpenRecordSet("myTable") 'myTable is a MS-Access table created previously

'populate the table
rs.movelast
rs.movefirst

do while not rs.EOF
   debug.print(rs!myField) 'myField is a field name in table myTable
   rs.movenext             'press Ctrl+G to see debuG window beneath
loop

msgbox("End of Table")

end sub

您可以通过不同方式交互查询和过滤表等数据对象：

通过查询：

private sub showQueryData

dim db as dao.database
dim rs as dao.recordset
dim sqlStr as string

sqlStr = "SELECT * FROM customers as c WHERE c.country='Brazil'"

set db = currentDb
set rs = db.openRecordset(sqlStr)

rs.movefirst

do while not rs.EOF
  debug.print("cust ID: " & rs!id & " cust name: " & rs!name)
  rs.movenext
loop

msgbox("End of customers from Brazil")

end sub

您还应该寻找记录集对象的“过滤器”属性以仅过滤所需的记录，然后以相同的方式与它们交互（参见 MS-Access 代码窗口中的 VB6 帮助），或创建一个“QueryDef”对象运行查询并将其也用作记录集（有点棘手）。如果你想要另一种方法，请告诉我。

我希望我有所帮助。

【讨论】：

一些 cmets：在 .MoveFirst 之前执行 .MoveLast 没有任何好处，除非您需要准确的记录集记录数。否则，您只是在浪费资源遍历记录集的末尾并再次回到开头，没有任何目的。

我看不出过滤现有记录集有什么用处。该过程的昂贵部分是打开记录集。如果您需要记录子集，请从该过滤器开始。否则，过滤记录集然后对结果进行处理没有多大意义。

您好 David-W-Fenton，感谢您的建议。我只是认为，对于小型表，填充记录集值得将数据加载到内存中并提高 seek 等方法的速度。 Access 帮助中也会显示将记录集移动到其末尾然后再到其开头。

我认为你已经把它弄反了——记录集越小，将它加载到记录集中的价值就越小，因为 Jet 会将整个小表缓存在内存中。应该避免 SEEK，因为它实际上没有任何用处，除非在非常特殊的情况下非常小。

当你用完rs.close记录集和db.close数据库是个好主意。

【参考方案3】：

找到了一个用 cmets 解释每个语句的好代码。 代码位于 - accessallinone

Sub DAOLooping()
On Error GoTo ErrorHandler

Dim strSQL As String
Dim rs As DAO.Recordset

strSQL = "tblTeachers"
'For the purposes of this post, we are simply going to make 
'strSQL equal to tblTeachers.
'You could use a full SELECT statement such as:
'SELECT * FROM tblTeachers (this would produce the same result in fact).
'You could also add a Where clause to filter which records are returned:
'SELECT * FROM tblTeachers Where ZIPPostal = '98052'
' (this would return 5 records)

Set rs = CurrentDb.OpenRecordset(strSQL)
'This line of code instantiates the recordset object!!! 
'In English, this means that we have opened up a recordset 
'and can access its values using the rs variable.

With rs


    If Not .BOF And Not .EOF Then
    'We don’t know if the recordset has any records, 
    'so we use this line of code to check. If there are no records 
    'we won’t execute any code in the if..end if statement.    

        .MoveLast
        .MoveFirst
        'It is not necessary to move to the last record and then back 
        'to the first one but it is good practice to do so.

        While (Not .EOF)
        'With this code, we are using a while loop to loop 
        'through the records. If we reach the end of the recordset, .EOF 
        'will return true and we will exit the while loop.

            Debug.Print rs.Fields("teacherID") & " " & rs.Fields("FirstName")
            'prints info from fields to the immediate window

            .MoveNext
            'We need to ensure that we use .MoveNext, 
            'otherwise we will be stuck in a loop forever… 
            '(or at least until you press CTRL+Break)
        Wend

    End If

    .close
    'Make sure you close the recordset...
End With

ExitSub:
    Set rs = Nothing
    '..and set it to nothing
    Exit Sub
ErrorHandler:
    Resume ExitSub
End Sub

记录集在循环数据时有两个重要的属性，EOF（文件结束）和 BOF（文件开始）。记录集就像表格，当您遍历一个表格时，您实际上是按顺序从一个记录移动到另一个记录。在您浏览记录时，EOF 属性设置为 false，但在您尝试越过最后一条记录后，EOF 属性变为 true。对于 BOF 属性，这同样适用。

这些属性让我们知道何时达到记录集的限制。