C#

string query = "SELECT A.emp_id, A.emp_first_name, A.emp_last_name, B.vehicle_no FROM (SELECT emp_id, emp_first_name, emp_last_name FROM emp_detail WHERE (emp_id = (SELECT emp_id FROM Tag_Assign WHERE(Tag_no =(select tag_no from tag_master where tag_id='" + textBox2.Text.Trim() + "'))))) AS A CROSS JOIN (SELECT emp_id, vehicle_no FROM Tag_Assign AS Tag_Assign_1 WHERE(Tag_no =(select tag_no from tag_master where tag_id='" + textBox2.Text.Trim() + "'))) AS B";

DataTable dt = con.datasource(query.Trim());

if (dt.Rows.Count > 0)
{
   lblEmp_name.Text = dt.Rows[0][1].ToString() + " " + dt.Rows[0][2].ToString();

   lblVehicle_no.Text = dt.Rows[0][3].ToString();
}

SELECT 
    ED.emp_id, 
    ED.emp_first_name, 
    ED.emp_last_name,
    TA.vehicle_no
FROM 
    emp_detail As ED
    INNER JOIN Tag_Assign As TA
    ON TA.emp_id = ED.emp_id
    INNER JOIN tag_master As TM
    ON TA.Tag_no = TM.tag_no
WHERE 
    TM.tag_id = @tag_id

<appSettings>
  <add key ="SomeKey" value="Somevalue"/>
</appSettings>

string valueFromConfig = ConfigurationManager.AppSettings["SomeKey"];