如何从 Access 数据库 VB.net 中检索特定数据？

Question

我正在尝试从具有所选客户 ID 的客户帐户数据库中检索特定值。我不确定该怎么做，这是我目前所知道的。

我将从组合框中选择客户 ID，那么我将如何在我的代码中用 SQL 准确地声明它？

Dim con As New OleDbConnection 'a new connection for the database is assigned 
        con.ConnectionString = "Provider =Microsoft.ACE.OLEDB.12.0; data source= C:\Users\Hamza\Documents\POS system1.accdb "
        con.Open()


        Dim cmd As OleDbCommand
        Dim dr As OleDbDataReader

        cmd = New OleDbCommand("Select Points from customers WHERE CustID= @CustID", con)  'query used to select all field
        dr = cmd.ExecuteReader

        txtdiscount.Text = Convert.ToInt32(dr)

        con.Close()

Answer 1

不要将数据库代码与用户界面代码混在一起。

连接和命令应该调用它们的 Dispose 方法，以便它们可以释放非托管资源。 Using...End Using 块将为您处理此问题（并关闭连接）。您需要为 @ID.

添加一个参数

ExecuteScalar 的使用在评论中解决。

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim ID = CInt(ComboBox1.SelectedItem)
    Dim Points = GetPointsByID(ID)
    txtdiscount.Text = Points
End Sub

Private Function GetPointsByID(ID As Integer) As String
    Dim pts As String = ""
    Using con As New OleDbConnection("Provider =Microsoft.ACE.OLEDB.12.0; data source= C:\Users\Hamza\Documents\POS system1.accdb "),
            cmd As New OleDbCommand("Select Points from customers WHERE CustID= @CustID", con)
        cmd.Parameters.Add("@CustID", OleDbType.Integer).Value = ID
        con.Open()
        pts = CStr(cmd.ExecuteScalar)
    End Using
    Return pts
End Function

如何从 Access 数据库 VB.net 中检索特定数据？

How to retrieve specific data from Access database VB.net?

sql

database

vb.net

ms-access