含有参数变量的sql语句，如何用C#语句表示。

         private void button1_Click(object sender, EventArgs e)
        {
            string mystr;
            SqlConnection myconn = new SqlConnection();
            DataSet myds = new DataSet();
            mystr = "Data Source =.;Initial Catalog = school;Integrated Security = True";
            myconn.ConnectionString = mystr;
            myconn.Open();

            string mysql = "SELECT Cname,Grade FROM student,score,course WHERE student.Sno = score.Sno" +
                    "and score.Cno = course.Cno and student.Sno =" + Convert.ToString(textBox1.Text) +
                    "and score.Text =" + Convert.ToInt32(comboBox1.Text);

            SqlDataAdapter myda = new SqlDataAdapter(mysql, myconn);
            myda.Fill(myds, "school");
            myconn.Close();
            DataView mydv = new DataView(myds.Tables["school"]);

            listBox1.Items.Add("课程名\t\t\t\t成绩");
            for (int i = 0; i < mydv.Count; i++)
            {
                listBox1.Items.Add(String.Format("{0}\t\t\t{1}", mydv[i]["Cname"],
                    mydv[i]["Grade"]));
            }

        }
程序在运行时没有结果显示在listbox1中，能帮我看看错哪了。 C# sql 变量 --------------------编程问答-------------------- sql语句的问题

string mysql = "SELECT Cname,Grade FROM student,score,course WHERE student.Sno = score.Sno" +
            " and score.Cno = course.Cno and student.Sno =" + Convert.ToString(textBox1.Text) +
            " and score.Text =" + Convert.ToInt32(comboBox1.Text);
        --换行后 and 的前面应该是空格 --------------------编程问答-------------------- 拼接有问题
"and score.Cno = course.Cno and student.Sno =" + Convert.ToString(textBox1.Text)
这里  你不妨断定看一看  你整句的sql  是不是在这里  student.sno= 后面的其实是个字符换  但是在数据库里应该是'字符串' 这样的格式  你应该是报语法错误的问题   --------------------编程问答-------------------- 建议改成   "and score.Cno = course.Cno and student.Sno = '" + Convert.ToString(textBox1.Text)+"'" 这样 --------------------编程问答-------------------- 这一串拼接多难看啊，去msdn看下sqlParameter用法
http://social.msdn.microsoft.com/Search/zh-CN?query=sqlParameter&ac=2
[code=sql]

补充：.NET技术 ,  C#