OR statement in SQL command does not function - sql

Question

Does anyone know to fix the error? I would like to create the OR statement but it does not function in my code. The code is shown below. I have removed the OR to see the code function or not, it can function if I remove the or statement. So I desperately want to know what the real problem with my code is.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;
public partial class updateform : System.Web.UI.Page
{
protected void Button1_Click(object sender, EventArgs e)
{
SqlConnection con = new SqlConnection("Data Source=.\\sqlexpress;Initial Catalog=test;Integrated Security=True");
SqlDataAdapter sda = new SqlDataAdapter("Select * FROM [EMP] WHERE Serial_Num='" + TextBox2.Text + "' or Equipment_ID ='" + TextBox1.Text + "'", con);
DataTable dt = new DataTable();
sda.Fill(dt);
TextBox3.Text = dt.Rows[0][2].ToString();
TextBox4.Text = dt.Rows[0][6].ToString();
DropDownList1.Text = dt.Rows[0][7].ToString();
TextBox5.Text = dt.Rows[0][18].ToString();
TextBox6.Text = dt.Rows[0][11].ToString();
TextBox11.Text = dt.Rows[0][8].ToString();
TextBox7.Text = dt.Rows[0][20].ToString();
TextBox12.Text = dt.Rows[0][17].ToString();
DropDownList2.Text = dt.Rows[0][23].ToString();
TextBox9.Text = dt.Rows[0][14].ToString();
TextBox10.Text = dt.Rows[0][13].ToString();
TextBox13.Text = dt.Rows[0][12].ToString();
TextBox2.Text = dt.Rows[0][5].ToString();
TextBox1.Text = dt.Rows[0][4].ToString();
}
protected void Button2_Click(object sender, EventArgs e)
{
SqlConnection con = new SqlConnection("Data Source =.\\sqlexpress; Initial Catalog = test; Integrated Security = True");
con.Open();
SqlCommand cmd = new SqlCommand(#"UPDATE EMP SET Model='" + TextBox3.Text + "' ,Description= '" + TextBox4.Text + "' ,Location='" + DropDownList1.Text + "',Manufacturer_or_Vendor= '" + TextBox5.Text + "',NCR_or_OOT_History='" + TextBox6.Text + "',Due_date= '" + TextBox11.Text + "' ,Year_of_Manufacturing='" + TextBox12.Text + "',Asset_No= '" + TextBox7.Text + "' ,Status='" + DropDownList2.Text + "',Responsible_Person= '" + TextBox9.Text + "',Available_in_Sapphire= '" + TextBox10.Text + "',Last_OOT_issuance_Date= '" + TextBox13.Text + "' WHERE (Serial_Num = '" + TextBox2.Text + "' or Equipment_ID = '" + TextBox1.Text + "' )", con);
cmd.ExecuteNonQuery();
con.Close();
}
protected void Page_load(object sender, EventArgs e)
{
if (!IsPostBack)
{
Calendar1.Visible = false;
Calendar2.Visible = false;
Calendar3.Visible = false;
}
}
protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
{
if (Calendar1.Visible)
{
Calendar1.Visible = false;
}
else
{
Calendar1.Visible = true;
}
}
protected void ImageButton2_Click(object sender, ImageClickEventArgs e)
{
if (Calendar2.Visible)
{
Calendar2.Visible = false;
}
else
{
Calendar2.Visible = true;
}
}
protected void ImageButton3_Click(object sender, ImageClickEventArgs e)
{
if (Calendar3.Visible)
{
Calendar3.Visible = false;
}
else
{
Calendar3.Visible = true;
}
}
protected void Calendar1_SelectionChanged(object sender, EventArgs e)
{
TextBox11.Text = Calendar1.SelectedDate.ToString("dd/MM/yyyy");
Calendar1.Visible = false;
}
protected void Calendar2_SelectionChanged(object sender, EventArgs e)
{
TextBox12.Text = Calendar2.SelectedDate.ToString("dd/MM/yyyy");
Calendar2.Visible = false;
}
protected void Calendar3_SelectionChanged(object sender, EventArgs e)
{
TextBox13.Text = Calendar1.SelectedDate.ToString("dd/MM/yyyy");
Calendar3.Visible = false;
}
protected void Calendar1_DayRender(object sender, DayRenderEventArgs e)
{
if (e.Day.IsOtherMonth)
{
e.Day.IsSelectable = false;
}
}
protected void Calendar2_DayRender(object sender, DayRenderEventArgs e)
{
if (e.Day.IsOtherMonth)
{
e.Day.IsSelectable = false;
}
}
protected void Calendar3_DayRender(object sender, DayRenderEventArgs e)
{
if (e.Day.IsOtherMonth)
{
e.Day.IsSelectable = false;
}
}
protected void Button3_Click(object sender, EventArgs e)
{
Response.Redirect("Default.aspx");
}
}

Answer 1

It is not clear from your description whether it fails at compile time or execution time, or what the error is. But a wild guess of what could be the problem, try the followings:
Instead of Select * try specifying the actual columns (like select col1, col2, ..
Instead of:
sda.Fill(dt);
Declare a dataset and fill the dataset and see if it works.
DataSet ds = new DataSet ();
sda.Fill (ds);
If this works, check and see how many tables are created in your dataset and what records are in each table.