堆栈(Stack)就是栈 select OrderSn from ORDER_Tracking group by OrderSn having count(1)>=2 HttpClient httpclient = new HttpClient(); var ret = httpclient.GetAsync("https://www.baidu.com/"); var Content = ret.Result.Content.ReadAsStringAsync().Result; UTF-8编码的文字可以在各国各种支持UTF-8字符集的浏览器上显示

// DateTime是值类型,datetime1 是开辟了一个地址 // datetime2 = datetime1 将datetime1赋值给datetime2 datetime2 又开辟了一个新的空间 // datetime1 和datetime2 是两个不同的地址内存空间 // 所以改变了time1的值,是不会改变time2的值 // 这就是值类型的特点 ：开辟俩地址空间 var datetime1 = DateTime.Now; var datetime2 = datetime1; DateTime * p1 = & datetime1; DateTime * p2 = & datetime2; datetime1 = datetime1.AddDays( 3 ); DateTime * p3 = & datetime1; DateTime * p4 = & datetime2; int str1 = 100 ; int str2 = str1; int * s1 = & str1; int * s2 = & str2; str1 = str1 + 100 ; int * s3 = & str1; int * s4 = & str2;