帮我写一个 用ajax实现增删改查前后端,，使用html文件、js文件中应用ajax为前端，一般处理程序ashx为后端，使用SqlServer数据库

好的，我明白了，下面是对您的问题的回答：

首先，要实现增删改查功能，需要在SqlServer数据库中创建对应的表，并在后台ashx文件中编写对应的增删改查方法。以下是示例代码：

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;

namespace WebApplication1
{
    /// <summary>
    /// Handler 的摘要说明
    /// </summary>
    public class Handler : IHttpHandler
    {

        public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "text/plain";
            string action = context.Request.QueryString["action"];
            string result = "";
            switch (action)
            {
                case "add": // 添加数据
                    result = AddData(context.Request.Form["name"], context.Request.Form["age"], context.Request.Form["sex"]);
                    break;
                case "delete": // 删除数据
                    result = DeleteData(context.Request.QueryString["id"]);
                    break;
                case "update": // 更新数据
                    result = UpdateData(context.Request.Form["id"], context.Request.Form["name"], context.Request.Form["age"], context.Request.Form["sex"]);
                    break;
                case "query": // 查询数据
                    result = QueryData();
                    break;
                default:
                    break;
            }
            context.Response.Write(result);
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }

        // 添加数据
        private string AddData(string name, string age, string sex)
        {
            string connectionString = ConfigurationManager.ConnectionStrings["SqlServer"].ConnectionString;
            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                conn.Open();
                string sql = "INSERT INTO UserInfo (Name, Age, Sex) VALUES (@Name, @Age, @Sex)";
                using (SqlCommand cmd = new SqlCommand(sql, conn))
                {
                    cmd.Parameters.AddWithValue("@Name", name);
                    cmd.Parameters.AddWithValue("@Age", age);
                    cmd.Parameters.AddWithValue("@Sex", sex);
                    int result = cmd.ExecuteNonQuery();
                    if (result > 0)
                    {
                        return "添加成功！";
                    }
                    else
                    {
                        return "添加失败！";
                    }
                }
            }
        }

        // 删除数据
        private string DeleteData(string id)
        {
            string connectionString = ConfigurationManager.ConnectionStrings["SqlServer"].ConnectionString;
            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                conn.Open();
                string sql = "DELETE FROM UserInfo WHERE Id = @Id";
                using (SqlCommand cmd = new SqlCommand(sql, conn))
                {
                    cmd.Parameters.AddWithValue("@Id", id);
                    int result = cmd.ExecuteNonQuery();
                    if (result > 0)
                    {
                        return "删除成功！";
                    }
                    else
                    {
                        return "删除失败！";
                    }
                }
            }
        }

        // 更新数据
        private string UpdateData(string id, string name, string age, string sex)
        {
            string connectionString = ConfigurationManager.ConnectionStrings["SqlServer"].ConnectionString;
            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                conn.Open();
                string sql = "UPDATE UserInfo SET Name = @Name, Age = @Age, Sex = @Sex WHERE Id = @Id";
                using (SqlCommand cmd = new SqlCommand(sql, conn))
                {
                    cmd.Parameters.AddWithValue("@Id", id);
                    cmd.Parameters.AddWithValue("@Name", name);
                    cmd.Parameters.AddWithValue("@Age", age);
                    cmd.Parameters.AddWithValue("@Sex", sex);
                    int result = cmd.ExecuteNonQuery();
                    if (result > 0)
                    {
                        return "修改成功！";
                    }
                    else
                    {
                        return "修改失败！";
                    }
                }
            }
        }

        // 查询数据
        private string QueryData()
        {
            string connectionString = ConfigurationManager.ConnectionStrings["SqlServer"].ConnectionString;
            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                conn.Open();
                string sql = "SELECT * FROM UserInfo";
                using (SqlCommand cmd = new SqlCommand(sql, conn))
                {
                    DataTable dataTable = new DataTable();
                    SqlDataAdapter adapter = new SqlDataAdapter(cmd);
                    adapter.Fill(dataTable);
                    string jsonStr = DataTableToJson(dataTable);
                    return jsonStr;
                }
            }
        }

        // DataTable转换为JSON字符串
        private string DataTableToJson(DataTable table)
        {
            System.Web.Script.Serialization.JavaScriptSerializer jss = new System.Web.Script.Serialization.JavaScriptSerializer();
            List<Dictionary<string, object>> list = new List<Dictionary<string, object>>();
            foreach (DataRow dataRow in table.Rows)
            {
                Dictionary<string, object> dict = new Dictionary<string, object>();
                foreach (DataColumn column in table.Columns)
                {
                    dict[column.ColumnName] = dataRow[column];
                }
                list.Add(dict);
            }
            return jss.Serialize(list);
        }
    }
}

接下来，需要在html中编写前端页面，使用jquery库来调用服务端的ashx方法，实现增删改查功能。以下是示例代码：

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta charset="utf-8" />
    <title></title>
    <script src="Scripts/jquery-1.11.1.min.js"></script>
    <script>
        $(document).ready(function () {
            loadData();
            $("#btnAdd").click(function () {
                var name = $("#txtName").val();
                var age = $("#txtAge").val();
                var sex = $("#selSex").val();
                $.ajax({
                    type: "POST",
                    url: "Handler.ashx?action=add",
                    data: { "name": name, "age": age, "sex": sex },
                    dataType: "text",
                    success: function (data) {
                        alert(data);
                        loadData();
                    },
                    error: function (err) {
                        alert(err);
                    }
                });
            });
            $("#btnUpdate").click(function () {
                var id = $("#txtId").val();
                var name = $("#txtName").val();
                var age = $("#txtAge").val();
                var sex = $("#selSex").val();
                $.ajax({
                    type: "POST",
                    url: "Handler.ashx?action=update",
                    data: { "id": id, "name": name, "age": age, "sex": sex },
                    dataType: "text",
                    success: function (data) {
                        alert(data);
                        loadData();
                    },
                    error: function (err) {
                        alert(err);
                    }
                });
            });
            $("#tbody").on("click", ".btnDelete", function () {
                var id = $(this).attr("data-id");
                if (confirm("确定要删除该记录吗？")) {
                    $.ajax({
                        type: "GET",
                        url: "Handler.ashx?action=delete",
                        data: { "id": id },
                        dataType: "text",
                        success: function (data) {
                            alert(data);
                            loadData();
                        },
                        error: function (err) {
                            alert(err);
                        }
                    });
                }
            });
        });
        function loadData() {
            $.ajax({
                type: "GET",
                url: "Handler.ashx?action=query",
                dataType: "json",
                success: function (data) {
                    var tbody = $("#tbody");
                    tbody.empty();
                    $.each(data, function (index, item) {
                        var tr = $("<tr>");
                        var tdId = $("<td>").html(item.Id);
                        var tdName = $("<td>").html(item.Name);
                        var tdAge = $("<td>").html(item.Age);
                        var tdSex = $("<td>").html(item.Sex);
                        var tdOperate = $("<td>").html("<a href='#' class='btnDelete' data-id='" + item.Id + "'>删除</a>");
                        tr.append(tdId).append(tdName).append(tdAge).append(tdSex).append(tdOperate);
                        tbody.append(tr);
                    });
                },
                error: function (err) {
                    alert(err);
                }
            });
        }
    </script>
</head>
<body>
    <table border="1">
        <thead>
            <tr>
                <th>ID</th>
                <th>姓名</th>
                <th>年龄</th>
                <th>性别</th>
                <th>操作</th>
            </tr>
        </thead>
        <tbody id="tbody">
        </tbody>
    </table>
    <div style="margin-top: 20px;">
        <input type="hidden" id="txtId" />
        <input type="text" id="txtName" placeholder="姓名" />
        <input type="text" id="txtAge" placeholder="年龄" />
        <select id="selSex">
            <option value="男">男</option>
            <option value="女">女</option>
        </select>
        <button id="btnAdd">添加</button>
        <button id="btnUpdate">修改</button>
    </div>
</body>
</html>

这样，一个使用ajax实现增删改查的前后端页面就完成了。如果需要修改数据库连接字符串，只需要在Web.config中修改即可。