利用AJAX验证输入的用户名在sqlserver数据库中是否已经存在

HtmlPage.html：


<html>
<head>
    <meta charset="utf-8" />
    <title></title>
    <script type="text/javascript">
        var xmlHttp;
        function Validation() {

            if (window.XMLHttpRequest) {
                xmlHttp = new XMLHttpRequest();
            } else {
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            }
            var name = document.getElementById("Text1");
            xmlHttp.open("Get", "Default2.aspx?name=" + name.value);
            xmlHttp.onreadystatechange= onmessageBack;
            xmlHttp.send(null);
        }

        function onmessageBack(){
            if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
                document.getElementById("result").innerHTML = xmlHttp.responseText;
            }
        }
    </script>
</head>
<body>
    <form id="form1" runat="server">
        请在下面的文本框中输入用户名，进行检验<br />
        用户名：
        <input id="Text1" type="text" onblur="Validation()" /><br />
        <div id="result"></div>

    </form>
</body>
</html>

Default2.aspx.cs：

private string myConnStr = ConfigurationManager.ConnectionStrings["SQL"].ConnectionString;
    protected void Page_Load(object sender, EventArgs e)
    {
        Response.Expires = -1;
        string name = this.Request.QueryString["name"];

        string mydr;
        SqlConnection myConn = new SqlConnection(myConnStr);
        string sql = "SELECT UserName from Users WHERE UserName=";
        sql = sql + "'" + name  + "'";
        SqlCommand sqlCommand = new SqlCommand(sql, myConn);
        try
        {
            myConn.Open();
            if (name != "")
            {
                if (sqlCommand.ExecuteScalar() != null)
                {
                    mydr = sqlCommand.ExecuteScalar().ToString();
                    Response.Write("该用户名已被注册，请返回重新注册！");
                    Response.End();
                }
                else
                {
                    Response.Write("该用户名可用。");
                    Response.End();
                }
            }
            else
            {
                Response.Write("请输入用户名！");
                Response.End();
            }
        }
        catch (SqlException se)
        {

            Response.Write(se.Message + "<br>");
            Response.End();
        }
        finally
        {
            myConn.Close();
        }
    }

Web.config:

<connectionStrings>
    <add name="SQL" connectionString="data source=DESKTOP-NA2OPPJ\SQLEXPRESS;database=users;user id=sa;pwd=123"/>
    
  </connectionStrings>

利用AJAX验证输入的用户名在sqlserver数据库中是否已经存在

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