c# - sql 数据库错误 "Must declare the scalar variable"

Question

我的登录系统有问题。我制作了一个运行良好的简单系统，但我想让它更高级，并根据用户的 UserType 显示不同的起始页。但是，我遇到了以下错误:“必须声明标量变量@UserType。”

using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

public partial class LoginwithEncryption : System.Web.UI.Page
{

    protected void btnSubmit_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["conStr"].ConnectionString);
        con.Open();
        SqlCommand cmd = new SqlCommand(
            "select * from dbo.UserInfo where Login =@Login and UserType=@UserType and Password=@Password and UserType=@UserType", con);
        cmd.Parameters.AddWithValue("@Login", txtUserName.Text);
        cmd.Parameters.AddWithValue("@Password", txtPWD.Text+".123");


        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        da.Fill(dt);

        if (dt.Rows.Count > 0)
        {
            int usertype = Convert.ToInt32(dt.Rows[0]["UserType"]);


            if (usertype == 1)
            {
                Response.Redirect("StartPage.aspx");
            }
            else if (usertype == 2)
            {
                Response.Redirect("DiferentStartPage.aspx");
            }

        }
        else
        {
            ClientScript.RegisterStartupScript(Page.GetType(), "validation",
                "<script language='javascript'>alert('Invalid UserName and Password')</script>");
        }

    }
}

Answer 1

如错误所述:必须声明标量变量“@UserType”

换句话说，SQL命令有一个参数为@UserType，但是参数集合中没有声明参数。

SqlCommand cmd = new SqlCommand(
"select * from dbo.UserInfo where Login =@Login and UserType=@UserType and Password=@Password and UserType=@UserType", con);
cmd.Parameters.AddWithValue("@Login", txtUserName.Text);
cmd.Parameters.AddWithValue("@Password", txtPWD.Text+".123");

为@UserType 参数添加另一个参数:

cmd.Parameters.AddWithValue("@UserType", "User Type");

此外，SQL 包含对 @UserType 的重复引用:

select * from dbo.UserInfo 
where Login=@Login 
      and UserType=@UserType 
      and Password=@Password 
      and UserType=@UserType

应该是:

select * from dbo.UserInfo 
where Login=@Login 
      and Password=@Password
      and UserType=@UserType