Question

Private Sub btn_ok_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_ok.Click
    mysqlconn.Open()
    cmd.CommandText = "select *  from login "
    cmd.Connection = mysqlconn
    dr = cmd.ExecuteReader
    dr.Read()

    If txtuser.Text = "" And txt_password.Text = "" Then
        MsgBox("Please enter user name and password", MsgBoxStyle.Information, "Login form")
    Else
        If txtuser.Text = "" Then
            MsgBox("Please select user name", MsgBoxStyle.Information, "Login form")
        Else
            If txt_password.Text = "" Then
                MsgBox("Please enter password", MsgBoxStyle.Information, "Login form")
                'If (dr.FieldCount > 0) Then

                'Dim i As Integer = dr(1)
                ' For i = 1 To dr.FieldCount

                'user = dr("user").ToString
                ' password = dr("password").ToString
            ElseIf ((txtuser.Text = '" & txt_username.text & "') And (txt_password.Text = '" & txt_password.text & "')) Then
          form2.Show()


            Else : MsgBox("Password missmatch.", vbCritical, "Invalid password")
            End If
        End If
        End If
    dr.Close()

    cmd.Dispose()

    mysqlconn.Close()
    mysqlconn.Dispose()

End Sub

我有一个表login.username和密码是两列。我试图从上面的代码中的登录表中获取应用程序中的用户名和密码，但我无法从登录表中获取第二行条目，因为我有两个rowrs（ 1）username = abc，passowrd = abc 2）username = xyz，password = xyz）如何在运行时获得第二次登录？感谢

Answer 1

您可以使用DataTable来保留所有行，也可以使用DataReader.Read将读者推进到下一条记录。

DataTable

Dim tblUsers = New DataTable
Using con = New MySql.Data.MySqlClient.MySqlConnection(conString)
    Using da = New MySql.Data.MySqlClient.MySqlDataAdapter("select *  from login", con)
        da.Fill(tblUsers)
    End Using
End Using

If tblUsers.Rows.Count > 1 Then
    Dim user = tblUsers.Rows(1).Field(Of String)("User")
    Dim password = tblUsers.Rows(1).Field(Of String)("Password")
End If

的DataReader：

Using con = New MySql.Data.MySqlClient.MySqlConnection(conString)
    Using cmd = New MySql.Data.MySqlClient.MySqlCommand("select *  from login", con)
        Using reader = cmd.ExecuteReader()
            If reader.Read Then
                ' first user '
                If reader.Read Then
                    ' second user '
                    Dim user = reader.GetString("User")
                    Dim password = reader.GetString("Password")
                End If
            End If
        End Using
    End Using
End Using

Answer 2

如果您的目的是检查这对夫妇（用户名，密码），那么，请在表格中搜索这对夫妇，而不是在DataReader中搜索。这里唯一的假设是这对夫妇（用户名，密码）在登录表中是唯一的。

在这种情况下，请在查询中使用两个参数：

cmd.CommandText = "SELECT * FROM login WHERE user = @username AND password = @password"
cmd.Parameters.Add(new SqlParameter("username", username))
cmd.Parameters.Add(new SqlParameter("password", password))

'then execute and check the results:
dr = cmd.ExecuteReader()
if dr.Read() then
  'login successful
else
  'login failed
end

如何在运行时从mysql数据库获取第二行？

2 个答案: