ADO.NET 连接SQL server 基本 SqlConnection SqlCommand ExecuteScalar executeReader sqlAdapter

static class SQLHelper
    {
        public static string constr = "";
        public static void getConstr()
        {
            constr=ConfigurationManager.ConnectionStrings["ZQDB"].ConnectionString;
        }

    }





static void Main(string[] args)
        {
            if(SQLHelper.constr=="")
            {
                SQLHelper.getConstr();
            }
            using (SqlConnection con = new SqlConnection(SQLHelper.constr))
            {
                //测试，打开连接
                //3.打开连接（如果打开数据连接没有问题，表示连接成功）
                con.Open();
                using (SqlCommand cmd=new SqlCommand())
                {
                    //cmd.CommandText = "select count(*) from Student;";
                    //cmd.Connection = con;
                    //string num=cmd.ExecuteScalar().ToString();
                    //Console.WriteLine(num);

                    cmd.CommandText = "select * from Student";
                    cmd.Connection = con;
                    SqlDataReader reader=cmd.ExecuteReader();
                    while(reader.Read())
                    {
                        Console.WriteLine(reader["number"]+"   "+reader["name"]);
                    }
                }


                string str= "select * from Student";
                using (SqlDataAdapter dadapter=new SqlDataAdapter(str,con))
                {
                    DataTable dt = new DataTable();
                    dadapter.Fill(dt);
                    foreach (DataRow item in dt.Rows)
                    {
                        Console.WriteLine(item[1].ToString()+"  "+item[2].ToString());
                    }
                }
                    Console.WriteLine("数据库连接成功");
                
                con.Close();

                
            }
            Console.WriteLine("断开连接");
            Console.ReadKey();

            Console.ReadKey();
        }