Question

我做了一个带有SQL Server表的注册页面，现在我想做一个注册页面。如何检查输入的值是否存在？

这是我的代码块：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;

public partial class index : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }

    protected void btnSignIN_Click(object sender, EventArgs e)
    {
        string str = "Data Source=(LocalDB)\\MSSQLLocalDB;";
        str += "AttachDbFilename=|DataDirectory|Database.mdf;";
        str += "Integrated Security= True";
        string userName = txtUserNameLogIN.Text;
        string password = txtPasswordLogIN.Text;
        SqlConnection c = new SqlConnection(str);
        SqlCommand cmd = new SqlCommand("SELECT UserName FROM [Table] WHERE UserName=@userName", c);
        cmd.Parameters.AddWithValue("@userName", userName);

    }
}

从这里，我不知道该怎么做......

任何帮助将不胜感激。

Answer 1

如果您想检查用户名是否已经存在，您只需使用EXISTS进行检查 - 如下所示：

if ($grade == 1  && $sumScore <= 5)
 {
   $textscore = 'Beginning';
 }
 if ($grade ==1 && ($sumScore>5 && $sumScore <=8)) 
  {
   $textScore = 'Intermediate';
  }

修改

附注，但非常重要 - 您正在处理Disposable对象，并考虑处理它们：

var cmd = new SqlCommand("SELECT COUNT(1) FROM [Table] WHERE UserName = @userName", c); cmd.Parameters.AddWithValue("@userName", userName); var existingCount = Convert.ToInt32(cmd.ExecuteScalar()); if (existingCount > 0) { // exists logic }

Answer 2

 protected void btnSignIN_Click(object sender, EventArgs e)
{
    string str = "Data Source=(LocalDB)\\MSSQLLocalDB;";
    str += "AttachDbFilename=|DataDirectory|Database.mdf;";
    str += "Integrated Security= True";
    string userName = txtUserNameLogIN.Text;
    string password = txtPasswordLogIN.Text;
    SqlConnection c = new SqlConnection(str);
    SqlCommand cmd = new SqlCommand("SELECT UserName FROM [Table] WHERE UserName=@userName", c);

    SqlDataReader reader = cmd.ExecuteReader();
if (reader.Read())
            MessageBox.Show("connected");
        else
            MessageBox.Show("failed to connect");

        c.Close();

}

C＃＆amp; SQL Server：如何进行签到检查

2 个答案: