如何在運行時從mysqldatabase獲取第二行？

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 

我有一個表login.username和密碼是兩個columns.I想從上面的代碼登錄表獲取應用程序的用戶名和密碼，但因爲我有兩個我無法獲取從登錄表第二行條目rowrs（1）username = abc，passowrd = abc 2）username = xyz，password = xyz） 我將如何在運行時獲得第二次登錄入口？ 謝謝

Answer 1

您可以使用DataTable來保存所有行或使用DataReader.Read將閱讀器推進到下一個記錄。

1. 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 
   

2. 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

如果你的目的是檢查對（用戶名，密碼），那麼，搜索夫婦在表而不是在DataReader中。這裏唯一的假設是這對夫妻（用戶名，密碼）在登錄表中是唯一的。

在這種情況下，在查詢中使用兩個參數：

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