多用户注册表 vb.net

Question

我有一个针对多个用户的用户注册表。这工作正常，除了代码无法识别是否已经存在用户名。我知道我的代码中有错误，但我无法纠正那个错误。

代码如下，任何人都可以帮我排序，如何为读者编写修改代码

Private Sub OK_Click(sender As Object, e As EventArgs) Handles OK.Click
Dim user, pass As String
user = UsernameTextBox.Text
pass = PasswordTextBox.Text
Dim connection1 As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;      Data Source=Credentials.mdb;")
Dim command As New OleDbCommand("SELECT [ID] FROM [Staff] WHERE [usernameField] = username AND [passwordField] = password", connection1)
Dim usernameParam As New OleDbParameter("username", Me.UsernameTextBox.Text)
Dim passwordParam As New OleDbParameter("password",   Me.PasswordTextBox.Text)
command.Parameters.Add(usernameParam)
command.Parameters.Add(passwordParam)
command.Connection.Open()
Dim reader As OleDbDataReader = command.ExecuteReader()
If reader.HasRows Then
MessageBox.Show("User Exist")
MyPlayer.SoundLocation = path & LogOnsound
PasswordTextBox.Text = ""
UsernameTextBox.Text = ""
ElseIf user = "" Or pass = "" Then
MsgBox("Please Fill The Boxs", , "Error")
Else
Dim connection As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Credentials.mdb;"
Using myconnection As New OleDbConnection(connection)
myconnection.Open()
Dim sqlq As String = "INSERT INTO [staff] ([username], [password]) VALUES (@user, @pass)"
Using cmd As New OleDbCommand(sqlq, myconnection)
cmd.Parameters.AddWithValue("@usernme", user)
cmd.Parameters.AddWithValue("@passwrd", pass)
cmd.ExecuteNonQuery()
MsgBox("User Registered!", , "register")
user = ""
pass = ""
End Using
End Using
End If
command.Connection.Close()
End Sub

Answer 1

看起来你有很多错误：

1. 您应该指定@username，而不仅仅是在SELECT语句中username，以便将其识别为参数。
2. 你为什么要在password上检查匹配？如果您这样做，人们可以使用相同的用户名，只是密码不同......你想要那个吗？
3. 在SELECT中，usernameField作为 Staff 表中的列名，但在INSERT中，username作为列名。是哪个？
4. 在INSERT中，指定参数@user，但在cmd.Parameters.AddWithValue语句中，您@usernme。