how to avoid to insert duplicate data in db.

Question

when i insert the data i have error exception." The connection was not closed. The connection's current state is open. "

 

here is my code.

 

 

protected void Button3_Click(object sender, EventArgs e)

{

SqlDataAdapter da;

string qry = "select * from salesmans_master where rankuser=" + salesuserid.Text;

da = new SqlDataAdapter(qry, con);

con.Open();

DataSet ds = new DataSet();

da.Fill(ds);

if (ds.Tables[0].Rows.Count > 0)

{

Label15.Text = "this salesid is already present.";

}

else

{

SqlCommand cmd = new SqlCommand("insert into salesmans_master(name,addressof,rankuser,rankcode)values('" + salesname.Text + "','" + salesadderss.Text + "','" + salesuserid.Text + "','" + DropDownList1.SelectedValue + "')", con);

try

{

con.Open();

cmd.ExecuteNonQuery();

Label15.Text = "data Inserted";

con.Close();

}

catch (Exception ex)

{

Label15.Text = ex.Message;

}

}