Question

Function Authenticate(ByVal UserName As String, ByVal Password As String)
    Dim con As New OleDbConnection(connectionstring)

    Dim cmdstring As String
    cmdstring = "SELECT username, password  FROM tblUsers where username = @user AND password = @pass"

    con.Open()

    Dim cmd As OleDbCommand = New OleDbCommand(cmdstring, con)

    cmd.Parameters.AddWithValue("@user", OleDbType.VarChar).Value = UserName
    cmd.Parameters.AddWithValue("@pass", OleDbType.VarChar).Value = Password

    Dim sdr As OleDbDataReader = cmd.ExecuteReader()
    If (sdr.HasRows) Then
        Authenticate = True
    Else
        Authenticate = False
    End If
    sdr.Close()
    con.Close()
    con = Nothing
    Return Authenticate
End Function

任何人都可以提供帮助，不知道为什么我一打到A scalar variable '@user' needs to be declared就会收到这句话：

Dim sdr As OleDbDataReader = cmd.ExecuteReader()

Answer 1

您需要输入值，而不是类型，并使用如下函数：

cmd.Parameters.AddWithValue("@user", UserName)
cmd.Parameters.AddWithValue("@pass", PassWord)

这将解决您的错误。在这里您有更多信息： Documentation

Answer 2

答案如下

cmdstring = "SELECT username, password  FROM tblUsers where username = ? AND password = ?"

con.Open()

Dim cmd As OleDbCommand = New OleDbCommand(cmdstring, con)

cmd.Parameters.AddWithValue("@user", UserName)
cmd.Parameters.AddWithValue("@pass", Password)

出于某种原因，？在查询中诀窍，addwithvalues还添加了值得尊重的值？在查询中，花了一段时间才找到这个，所以我想我会分享：）

Answer 3

字符串后 Dim cmdstring As String cmdstring =“SELECT用户名，密码FROM tblUsers，其中username = @user AND password = @pass”

cmdstring cmdstring.replace（“@ user”，“'”＆amp; UserName＆amp;“'”）.replace（“pPassWord”，“'”＆amp; PassWord＆amp;“'”）

将创建正确的查询

Answer 4

尝试将.ExecuteReader()更改为ExecuteNonQuery()

Dim sdr As OleDbDataReader = cmd.ExecuteNonQuery()

这是关于ExecuteReader, ExecuteNonQuery, ExecuteScalar ... When to use What?

的一个很好的解释

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4 个答案: