使用比较运算符号进行比较查询

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace 比较查询
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        
        private void Form1_Load(object sender, EventArgs e)
        {
            // TODO: 这行代码将数据加载到表“studentDataSet.student”中。您可以根据需要移动或删除它。
            this.studentTableAdapter.Fill(this.studentDataSet.student);
            //ComboBox comboBox1 = new ComboBox();
            comboBox1.Items.Add("大于260");
            comboBox1.Items.Add("大于270");
            comboBox1.Items.Add("大于280");
            comboBox1.Items.Add("大于290");
            
        }

        private void button1_Click(object sender, EventArgs e)
        {
            
            string str = string.Empty;
            switch (comboBox1.SelectedItem.ToString())
            {
                case "大于260":
                    str = ">260";
                    break;
                case "大于270":
                    str = ">270";
                    break;
                case "大于280":
                    str = ">280";
                    break;
                case "大于290":
                    str = ">290";
                    break;
            }
            SqlConnection con = new SqlConnection("server=localhost\\SQL2005;uid=sa;pwd=1111qq;database=student");
            SqlDataAdapter dap = new SqlDataAdapter("select *from student where stuScore"+str,con);
            DataSet ds = new DataSet();
            dap.Fill(ds,"score");
            dataGridView1.DataSource = ds.Tables["score"].DefaultView;
            //dataGridView1.DataBind();
        }
    }
}