access 数据库查询某字段未使用过的序号的VB程序

你可以使用以下的VB程序来查询Access数据库中某个字段未使用过的序号：

Imports System.Data.OleDb

Public Class Form1
    Private Sub btnQuery_Click(sender As Object, e As EventArgs) Handles btnQuery.Click
        Dim connectionString As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\YourDatabase.accdb" ' 替换为你的数据库路径
        Dim columnName As String = "YourColumnName" ' 替换为你的字段名

        Dim connection As New OleDbConnection(connectionString)
        connection.Open()

        ' 查询最大的序号
        Dim maxNumber As Integer = 0
        Dim queryMaxNumber As String = $"SELECT MAX({columnName}) FROM YourTableName"
        Dim commandMaxNumber As New OleDbCommand(queryMaxNumber, connection)
        Dim resultMaxNumber As Object = commandMaxNumber.ExecuteScalar()
        If Not IsDBNull(resultMaxNumber) Then
            maxNumber = CInt(resultMaxNumber)
        End If

        ' 查询未使用过的序号
        Dim availableNumber As Integer = 1
        For i As Integer = 1 To maxNumber + 1
            Dim queryNumber As String = $"SELECT COUNT(*) FROM YourTableName WHERE {columnName} = {i}"
            Dim commandNumber As New OleDbCommand(queryNumber, connection)
            Dim resultNumber As Integer = CInt(commandNumber.ExecuteScalar())
            If resultNumber = 0 Then
                availableNumber = i
                Exit For
            End If
        Next

        connection.Close()

        MessageBox.Show($"未使用过的序号为: {availableNumber}")
    End Sub
End Class

请注意替换代码中的数据库路径（connectionString）、字段名（columnName）和表名（YourTableName）为你实际使用的值。这段代码将查询指定字段中未使用过的序号，并将结果显示在一个消息框中。