ID的动态添加

一）：数据库存储为int型，在textbox里显示“01”，之后根据数据库里ID的情况显示下一行ID，比如，数据库里的ID最大值为“06”，则新打开界面时要在界面上显示“07”：

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写在前面的代码：

Private ds As New DataSet

Dim comid1 As Int32
Dim comid2 As Int32

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   Dim sql As String = "select max(表里的ID字段) from 表"
   Dim adt As New OleDbDataAdapter(sql, DBcon)
   ds.Clear()
   adt.Fill(ds)
   comid2 = ds.Tables(0).Rows(0)(0)
   comid2 = comid2 + 1
   Me.TextBox3.Text = comid2

此段代码要写在form_load 和相应按钮里，一个也不能少！

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二）：数据库存储为char型，在textbox里显示“c01”，之后根据数据库里ID的情况显示下一行ID，比如，数据库里的ID最大值为“c06”，则新打开界面时要在界面上显示“c07”：

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写在前面的代码：

Private ds As New DataSet

Dim comid1 As Int32
Dim comid2 As Int32

    Dim comchar As String
    Dim comchar1 As String = "c"
    Dim comchar2 As String = "0"

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Dim sql1 As String = "select count(表里的ID字段) as cTypeID from 表"
        Dim adt As New OleDbDataAdapter(sql1, DBcon)
        ds.Clear()
        adt.Fill(ds)
        comid1 = ds.Tables(0).Rows(0)(0)
        comid1 = comid1 + 1
        If comid1 <= 9 Then
            comchar = comchar1 & comchar2 & comid1
        Else
            comchar = comchar1 & comid1
        End If
        Me.TextBox1.Text = comchar

此段代码要写在form_load 和相应按钮里，一个也不能少！

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三）：数据库存储为char型，在textbox里显示“c01001”，之后根据数据库里ID的情况显示下一行ID，要根据下拉菜单选择表一里的name，再将其对应的ID（c01）显示在textbox里，后面的“001”为自增。(此代码的运行结果为后面三位一直在自增，即选择了c01001之后只能选择c02002，不能选择c02001)

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写在前面的代码：

Private ds As New DataSet

Dim comid As Int32
  Dim comchar As String
  Dim comchar1 As String = "0"
  Dim kuid As String

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DBcon.Open()
        Dim sqlStr As String = "select ID from TMMType where name = '" & Me.ComboBox.SelectedItem & "'"
        Dim adt4 As New OleDbDataAdapter(sqlStr, DBcon)
        ds.Clear()
        adt.Fill(ds)
        DBcon.Close()

        kuid = Trim(CStr(ds.Tables(0).Rows(0).Item("ID")))
        Dim sql1 As String = "select count(ID) as ID from TMMCom"
        Dim adt5 As New OleDbDataAdapter(sql1, DBcon)
        ds5.Clear()
        adt5.Fill(ds5)
        comid = ds5.Tables(0).Rows(0)(0)
        comid = comid + 1
        If comid <= 9 Then
            comchar = kuid & comchar1 & comchar1 & comid
        ElseIf 10 <= comid <= 99 Then
            comchar = kuid & comchar1 & comid
        ElseIf 100 <= comid <= 999 Then
            comchar = kuid & comid
        End If
        Me.TextBox1.Text = comchar

以上代码写在相应按钮和 ComboBox的SelectedIndexChanged 事件里！（必须全写！）

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三）做法二：（三层结构做的）

Public Function GetNewChangeStoreID(ByVal str As String) As String

Try

con = New OleDbConnection(constr)

If con.State = ConnectionState.Open Then

con.Close()

End If

con.Open()

Dim sqlstr As String = "select Max(right(cID,3)) from TMM_ChangeStore"

cmd = New OleDbCommand(sqlstr, con)

Dim read As OleDbDataReader = cmd.ExecuteReader()

read.Read()

If Not read.Item(0) Is DBNull.Value Then

Dim num As Integer = read.Item(0)

Return "D" & str & (num + 1).ToString("D3")

Else

Return "D" & str & "001"

End If

Catch ex As Exception

MsgBox(ex.Message.ToString)

Finally

If con.State = ConnectionState.Open Then

con.Close()

End If

End Try

End Function