ASP.NET 成功执行Update 的 ExecuteNonQuery() 返回值大于0，但是查看数据库却没有改变

 1 //真实姓名保存
 2 $("#TrueNameSaveBtn").click(function () {
 3     if ($("#TrueNameSaveText").val() != "") {
 4         //上传数据
 5         $.post("/Home/UpdateUserInfo", { "item": "TrueName", "data": $("#TrueNameSaveText").val() }, function (result) {
 6             if (result == "success") {
 7                 $("#TrueNameErrorMsg").text(" * 保存成功 *");
 8 
 9             } else if (result == "error") {
10                 $("#TrueNameErrorMsg").text(" * 保存失败 *");
11             }
12         });
13     } else {
14         $("#TrueNameErrorMsg").text(" * 文本框不能为空 *");
15 
16     }
17 });

 1  public ActionResult UpdateUserInfo(string item,string data)
 2         {
 3             if (Session["username"] != null)
 4             {
 5                 string sql = "Update UserInfo set @item = @data where (LoginId = @LoginId or Email = @LoginId)";
 6                 try
 7                 {
 8                     using (SqlConnection con = new SqlConnection(connStr))
 9                     {
10                         con.Open();
11                         using (SqlCommand cmd = con.CreateCommand())
12                         {
13                             cmd.CommandText = sql;
14                             cmd.Parameters.Add(new SqlParameter("@data", data));
15                             cmd.Parameters.Add(new SqlParameter("@item", item));
16                             cmd.Parameters.Add(new SqlParameter("@LoginId", (string)Session["username"]));
17 
18                             if (cmd.ExecuteNonQuery() > 0)
19                             {
20                                 return Content("success");
21                             }
22                             else
23                             {
24                                 return Content("error");
25                             }
26                         }
27                     }
28                 }
29                 catch (Exception e)
30                 {
31                     throw e;
32                 }
33             }
34             else
35             {
36                 return Content("error");
37             }
38         }