webservice1.asmx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;

namespace work058
{
    /// <summary>
    /// WebService1 的摘要说明
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]
    // 若要允许使用 ASP.NET AJAX 从脚本中调用此 Web 服务，请取消注释以下行。 
    [System.Web.Script.Services.ScriptService]
    public class WebService1 : System.Web.Services.WebService
    {

        [WebMethod]
        public string HelloWorld()
        {
            return "Hello World";
        }

        [WebMethod(Description="检查用户表中是否已存在指定的用户名")]
        public bool ExistsUserName(string userName)
        {
            bool exists = false;

            System.Data.SqlClient.SqlConnectionStringBuilder bu = new System.Data.SqlClient.SqlConnectionStringBuilder();
            bu.DataSource = "(local)";
            bu.InitialCatalog = "test";
            bu.UserID = "sa";
            bu.Password = "123456";

            string conString = bu.ConnectionString;
            System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection(conString);
            con.Open();  //主动打开，要主动关闭，

            string sql = "select user_name from userinfo where user_name=@uName";
            System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand(sql, con);
            cmd.Parameters.AddWithValue("@uName",userName);

            System.Data.SqlClient.SqlDataReader reader = cmd.ExecuteReader(System.Data.CommandBehavior.CloseConnection);  //行为，附带关闭，就不用主动关闭数据库连接
            if (reader.HasRows)
            {
                exists = true;
            }
            else
            {
                exists = false;
            }
            reader.Close(); //这里关闭reader时，一并关闭了con
            return exists;
        }

        [WebMethod(Description="获取服务器的当前时间")]
        public DateTime GetServerTime()
        {
            return DateTime.Now;
        }
    }
}

web.config

<?xml version="1.0" encoding="utf-8"?>

<!--
  有关如何配置 ASP.NET 应用程序的详细信息，请访问
  http://go.microsoft.com/fwlink/?LinkId=169433
  -->

<configuration>
    <system.web>
      <compilation debug="true" targetFramework="4.5" />
      <httpRuntime targetFramework="4.5" />
    </system.web>
    <system.webServer>
        <directoryBrowse enabled="true" />
    </system.webServer>

</configuration>

sql

create database test;

create table UserInfo(
	user_id int identity(1,1) not null,
	user_name varchar(20) not null unique,
	real_name nvarchar(8) not null,
	age tinyint not null,
	sex bit not null,
	mobile varchar(14),
	phone varchar(14),
	email varchar(50) not null,
	primary key(user_id) 
);

insert into UserInfo values('zhangfei','张飞',36,1,'13011110001','8845996','zf@qq.com');
insert into UserInfo values('guanyu','关羽',38,1,'13011110002','8845995','gy@qq.com');
insert into UserInfo values('liubei','刘备',42,1,'13011110003','8845994','lb@qq.com');
insert into UserInfo values('zhaoyun','赵云',32,1,'13011110004','8845993','zy@qq.com');
insert into UserInfo values('huangzhong','黄忠',50,1,'13011110005','8845992','hz@qq.com');
insert into UserInfo values('caocao','曹操',48,1,'13011110006','8845991','cc@qq.com');
insert into UserInfo values('sunquan','孙权',33,1,'13011110007','8845990','sq@qq.com');
insert into UserInfo values('diaochan','貂蝉',20,0,'13011110008','8845880','dc@qq.com');
insert into UserInfo values('daqiao','大乔',21,0,'13011110009','8845881','dq@qq.com');
insert into UserInfo values('xiaoqiao','小乔',20,0,'13011110010','8845882','xq@qq.com');