黑马程序员 DONET连接数据库

 

　　　　　　　//IDisposible
            //using(类型 d = new ....)
            //{.....................}
            //SqlConnection为建立和数据库连接的对象
            //using (SqlConnection conn = new SqlConnection(
            //    "Data Source=127.0.0.1; Initial Catalog=MyTest;User ID=sa;Password=123456"))
            //{
            //    conn.Open();//打开连接
            //    //通过连接创建一个向数据库发命令（Command）的对象SqlCommand
            //    using (SqlCommand cmd = conn.CreateCommand())
            //    {
            //        //CommandText为要执行的SQL语句

            //        cmd.CommandText = "Insert into T_Student(Name,Age) values('元芳',2100)";
            //        cmd.ExecuteNonQuery();//执行
            //    }                
            //}

            //ExecuteNonQuery一般用来执行Update、Delete、Insert语句

            using (SqlConnection conn = new SqlConnection("Data Source=127.0.0.1; Initial Catalog=MyTest;User ID=sa;Password=123456"))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    //cmd.CommandText = "select count(*) from T_Student where Age<100";
                    //int i =  (int)cmd.ExecuteScalar();
                    //MessageBox.Show(i+"条数据");

                    //cmd.CommandText = "select 'aaa'";
                    ////ExecuteScalar一般用来执行有且只有一行一列返回值的SQL语句
                    //string s = (string)cmd.ExecuteScalar();
                    //MessageBox.Show(s);

                    //获得自增字段的值
                    //cmd.CommandText = "insert into T_Student(Name,Age) values('aaa',123) ;select @@identity";
                   // cmd.CommandText = "insert into T_Student(Name,Age) output inserted.Id values('aaa',123) ";
                    long i = (long)cmd.ExecuteScalar();//bigint→long
                    MessageBox.Show(i.ToString());
                }
            }