三层架构中DAL层Sqlhelper怎样快速掌握？（常用）

<add name="ProDBConnectionString" connectionString="Data Source=.;Initial Catalog=ProDB;Integrated Security=True"
            providerName="System.Data.SqlClient" />

 public class SqlHelper
    {
        //固定连接字符串
        public static string strcon = ConfigurationManager.ConnectionStrings["ProDBConnectionString"].ConnectionString;

        /// <summary>
        /// 查询
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public static DataTable Cx(string sql)
        {
            DataTable dt=new DataTable();
            SqlDataAdapter arAdapter=new SqlDataAdapter(sql,strcon);
            arAdapter.Fill(dt);
            return dt;
        }
        /// <summary>
        /// 增删改
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public static int Zsg(string sql)
        {
            int num = 0;
            SqlConnection sqlcon=new SqlConnection(strcon);
            SqlCommand cmd=new SqlCommand(sql,sqlcon);
            try
            {
                sqlcon.Open();
                num = cmd.ExecuteNonQuery();
            }
            finally
            {
                if (sqlcon.State==ConnectionState.Open)
                {
                    sqlcon.Close();
                }
            }

            return num;
        }
    }