DBHelper类 //一、两种身份验证:windows身份验证、SqlServer身份验证 string st1 = "server=.;database=orderdinner;Integrated Security = true"; string st2 = "server=.;database=hw;uid=sa;pwd=123"; //二、创建连接对象connection,两种连接方式:1.通过构造函数直接传身份验证字符串2.通过连接对象的属性的赋值来连接 // SqlConnection connection1 = n