无论我怎么查询，查出来的都是空的，逐步调试发现dt也是空的，请问该如何改正？  

private void button2_Click(object sender, EventArgs e)//点击按钮查询
        {
            string shijian = events.Text.Trim();//读取文本框的值
            string con_str = @"Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=D:\C#测试\LOGIN\LOGIN\BIN\DEBUG\WORKEVENTS.MDF;Integrated Security=True";
               string query =String.Format( "select events,recorddate,finishdate,department,supplier,price from workevensts where events={0}", @" ' " + shijian + @"% ' ");
            SqlConnection conn = new SqlConnection(con_str);
            SqlCommand cmd = new SqlCommand(query,conn);
             = query;
            SqlDataAdapter ada = new SqlDataAdapter();//数据适配器，访问数据用的
            ada.SelectCommand = cmd;
            DataTable dt = new DataTable();
            ada.Fill(dt);
            dataGridView1.DataSource = dt;
        }
    }

[此贴子已经被作者于2018-9-25 20:36编辑过]

这是个基本问题，你把你的SQl语句复制到数据库管理工具中，执行一下，看一下有没有结果返回

是数据库没有打开  conn.open();

那你记得关闭

private void button2_Click(object sender, EventArgs e)//点击按钮查询
        {
            string shijian = events.Text.Trim();//读取文本框的值
            string con_str = @"Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=D:\C#测试\LOGIN\LOGIN\BIN\DEBUG\WORKEVENTS.MDF;Integrated Security=True";
               string query =String.Format( "select events,recorddate,finishdate,department,supplier,price from workevensts where events={0}", @" ' " + shijian + @"% ' ");
            SqlConnection conn = new SqlConnection(con_str);
            conn.Open();
            SqlCommand cmd = new SqlCommand(query,conn);
             = query;
            SqlDataAdapter ada = new SqlDataAdapter();//数据适配器，访问数据用的
            ada.SelectCommand = cmd;
            DataTable dt = new DataTable();
            ada.Fill(dt);
            conn.Close();
            dataGridView1.DataSource = dt;
        }
    }