SqlHelper

configuration:
  <appSettings>
    <add key="SQLConn" value="data source=[server].com;initial catalog=[db];user id=[id];password=[pssd]"/>
  </appSettings>

SqlHelper:

using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;

namespace SmartLockerWS.Class
{
    class sqlHelper1
    {
        public static string GetSqlConnectionString()
        {
            return ConfigurationManager.AppSettings["SQLConn"].ToString();
        }
        //适合增删改操作，返回影响条数
        public static int ExecuteNonQuery(string sql, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(GetSqlConnectionString()))
            {
                using (SqlCommand comm = conn.CreateCommand())
                {
                    try
                    {
                        conn.Open();
                        comm.CommandText = sql;
                        if(parameters!=null)
                            comm.Parameters.AddRange(parameters);
                        return comm.ExecuteNonQuery();
                    }
                    catch (Exception ex)
                    {
                        throw new Exception(ex.Message);
                    }
                    finally
                    {
                        if (conn != null && conn.State != ConnectionState.Closed)
                            conn.Close();
                    }

                }
            }
        }
        //查询操作，返回查询结果中的第一行第一列的值
        public static object ExecuteScalar(string sql, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(GetSqlConnectionString()))
            {
                using (SqlCommand comm = conn.CreateCommand())
                {
                    try
                    {
                        conn.Open();
                        comm.CommandText = sql;
                        if(parameters!=null)
                            comm.Parameters.AddRange(parameters);
                        return comm.ExecuteScalar();
                    }
                    catch (Exception ex)
                    {

                        throw new Exception(ex.Message);
                    }
                    finally
                    {
                        if (conn != null && conn.State != ConnectionState.Closed)
                            conn.Close();
                    }
                }
            }
        }
        //Adapter调整，查询操作，返回DataTable
        public static DataTable ExecuteDataTable(string sql, params SqlParameter[] parameters)
        {
            using (SqlDataAdapter adapter = new SqlDataAdapter(sql, GetSqlConnectionString()))
            {
                DataTable dt = new DataTable();
                if(parameters!=null)
                    adapter.SelectCommand.Parameters.AddRange(parameters);
                adapter.Fill(dt);
                return dt;
            }
        }

        public static DataSet ExecuteDataset(string sql, params SqlParameter[] parameters)
        {
            using (SqlDataAdapter adapter = new SqlDataAdapter(sql, GetSqlConnectionString()))
            {
                DataSet ds = new DataSet();
                if(parameters!=null)
                    adapter.SelectCommand.Parameters.AddRange(parameters);
                adapter.Fill(ds);
                return ds;
            }
        }
        public static SqlDataReader ExecuteReader(string sqlText, params SqlParameter[] parameters)
        {
            //SqlDataReader要求，它读取数据的时候有，它独占它的SqlConnection对象，而且SqlConnection必须是Open状态
            SqlConnection conn = new SqlConnection(GetSqlConnectionString());//不要释放连接，因为后面还需要连接打开状态
            SqlCommand cmd = conn.CreateCommand();
            conn.Open();
            cmd.CommandText = sqlText;
            if(parameters!=null)
                cmd.Parameters.AddRange(parameters);
            //CommandBehavior.CloseConnection当SqlDataReader释放的时候，顺便把SqlConnection对象也释放掉
            return cmd.ExecuteReader(CommandBehavior.CloseConnection);
        }
    }

}

Call function:

　　try{
                string sql = "select a.badge,a.ic_card,b.name,b.email from [asmuser].[dbo].[ATSCardNo] a left join [asmuser].[dbo].[Employee] b on a.badge = b.badge where a.ic_card = @cardno";
                SqlParameter para_cardno = new SqlParameter("@cardno", SqlDbType.VarChar, 10);
                para_cardno.Value = CardNo;
                SqlParameter[] parms = { para_cardno };
                DataTable dt = sqlHelper1.ExecuteDataTable(sql, parms); 
                if (dt.Rows.Count > 0)
                {  }

 　          }

catch (Exception ex)
            {   }