SQL SERVER表格dategridview查询

DateTime date1;
DateTime date2;
string dt1, dt2;
int dt3, dt4;

    private void dateTimePicker1_ValueChanged(object sender, EventArgs e)
    {
        date1 = dateTimePicker1.Value;
        dt1 = dateTimePicker1.Text;
    }

    private void dateTimePicker2_ValueChanged(object sender, EventArgs e)
    {
        //date2 = dateTimePicker2.Value;

        dt2 = dateTimePicker2.Text;


    }

    private void button2_Click(object sender, EventArgs e)
    {
        SqlConnection Conn = new SqlConnection();
        Conn.ConnectionString = "server=LAPTOP-HPPFDM96\\SQLEXPRESS;database=db_zunyioven ;uid=zunyi;pwd=222";
        //Conn.ConnectionString = "server=DESKTOP-5RTJQL1;database=db_zunyioven ;uid=sa;pwd=222";
        //onn.Open();
        String sql_str = "Select * from dbo.tb_1 where date between '" + dt1+ "' and '" + dt2 + "'";
        //String sql_str = "Select * from dbo.tb_1 where date between '" + date1 + "' and '" + date2 + "'" ;
       //select* from LoginLog where loginTime between '" + dateTimePicker1.Text + "' and '" + dateTimePicker2.Text + "'" 
        textBox1.Text = sql_str;
        MessageBox.Show(dt1);
        MessageBox.Show(dt2);
        SqlDataAdapter da = new SqlDataAdapter(sql_str, Conn);
        DataSet ds = new DataSet();
        da.Fill(ds,"dbo.tb_1");
        dataGridView1.DataSource = ds.Tables["dbo.tb_1"]; 



    }

```我用SQLSERVER创建了一个表格，列是id,datetime,name. C#连接好后，用select* from LoginLog where loginTime between '" + dateTimePicker1.Text + "' and '" + dateTimePicker2.Text + "'" 查询，数据库不显示，查idn和ame都正常，请指教。谢谢！

textBox1.Text = sql_str; 这个输出什么，sql合法么
date是关键字，需要转义加上方括号
条件对么，这个区间范围有数据么

dateTimePicker1.Text 和dateTimePicker2.Text 分别输出的是什么，代入到sql里面直接在数据库里查一下，看这个区间有内容吗

最简单的方法就是进行代码调试，将sql内容复制到数据库查询分析器里执行以下，然后在那儿分析比较快