Question

我有一个代码，但它没有用。我试图在label2中设置一个值，但它不起作用。请帮帮我。

Private Sub student_no_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles student_no.Click
    MySqlConnection = New MySqlConnection
    MySqlConnection.ConnectionString = "server = localhost; port=3307; user id = root; password = 1234; database = sample;"
    Dim READER As MySqlDataReader

    Try
        MySqlConnection.Open()
        Dim query As String
        query = " select id from sample.student where last_name = '" & txtlastname.Text & "' "
        Dim Command As New MySqlCommand(query, MySqlConnection)
        READER = Command.ExecuteReader
        Label2.Text = query.ToString

        MessageBox.Show("Student Number Generated")
        MySqlConnection.Close()

    Catch ex As Exception
        MessageBox.Show(ex.Message)
    Finally
        MySqlConnection.Dispose()

    End Try

End Sub

Answer 1

您在查询中使用.ToString，这是一个字符串。你应该做的是对READER对象的操作。

由于SELECT将始终返回结果列表，因此您必须按原样处理结果，例如......

While READER.Read()
  MessageBox.Show((READER.GetInt32(0)))
End While

.Read（）返回返回的行集中的下一个元素

Answer 2

If READER.Read() Then
    Label2.Text = READER.GetString(0)
End If

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2 个答案: