How to validate a duplicate value of textbox in asp.net while submit button

I have 3 text box's and a submit button when i enter the va开发者_Python百科lues and submit then values are entered in database .

but when i enter the same values and enter then those values are also entered.......This should not happen...I need a popup window showing there are duplicate values that you have entered.Please give the code for aspx and aspx.cs and data base. Please explain in breif

try
    {
        int result = Timesheet_BI.InsertCompanyInformation(txtCompanyName.Text, txtAddress.Text);
        if (result == -1)
        {
            txtCompanyName.Focus();
            txtCompanyName.Attributes["onfocus"] = "this.select();";
            string jv = "<script>alert('Error Details: Duplicate Entry of Company Name ');</script>";
            ScriptManager.RegisterClientScriptBlock(this, typeof(Page), "alert", jv, false);
            return;
            //Page.ClientScript.RegisterStartupScript(typeof(string), "My Script", "Duplicate Enteries");
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }

Why don;t you use a simple java script to check this. or use JQuery /getElementById to get the controls and do a simple comparison.

If you have a bunch of textboxes to compage, give something similar to all the textbox Eg Give a common prefix to all textbox controls and use JQuery to get all the textboxes starting with that prefix and do a regular comparison. http://api.jquery.com/attribute-contains-selector/#

Eg;
$(:contains(<prefix>,textbox').each
(
function()
{
// do the comparison
}
)