Validate the student id

Try:

using (SqlConnection con = new SqlConnection(strConnect))
    {
    con.Open();
    using (SqlCommand cmd = new SqlCommand("SELECT COUNT(iD) FROM myTable WHERE id=@ID", con))
        {
        cmd.Parameters.AddWithValue("@ID", textbox1.Text);
        int count - cmd.ExecuteScalar();
        if (count != 0)
            {
            // It exists.
            }
        else
            {
            // It doesn't exist
            }
        }
    }

try This



Create An Function which have bool return Type

public bool Validate_Id(int Id) //id=txtid.text
{
Open The Connection
string StrSQL = "select count(*) from Student where "+Id+"";
SqlCommand cmd = new SqlCommand(StrSQL, cn);

SqlDataReader dr;
dr = cmd.ExecuteReader();
dr.Read();
int i = 0;
if (dr.HasRows)
{
i = Convert.ToInt32(dr.GetValue(0).ToString());
}


if (i > 0)
{
return true;
}
else
{
return false;
}
}

if it return true then id Exist


Hope So It Will Help You