work with data in data base

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C#

i want to work with data base in C# with sql compact 3.5 but in each form one of query that related with on table is execute i click on button and see the correct result butif i change the condition and click on button the query execute with the the old condition and i see the old result it peer that the sqlcashed the old data
any one can help me???
this my code:

 private DataTable select(string con)
        {

            DataTable k = new System.Data.DataTable();
            try
            {

                string str = "Data Source=C:\\Documents and Settings\\almas\\Desktop\\BazarKhodro\\khodro.sdf";
                Qconnection.ConnectionString = str;
                Qcommand.Connection = Qconnection;
                Qcommand.Parameters.AddWithValue("@type", comboBox1 .Text );
                Qcommand.Parameters.AddWithValue("@name", textBox3.Text);
                Qcommand.Parameters.AddWithValue("@lname", textBox4.Text);
                string commandText = " select kharid.date, moshtari.name, moshtari.lname, kharid.type, kharid.modelfrom, kharid.modelto, kharid.tip, kharid.karkardfrom, kharid.karkardto, kharid.color, kharid.pricefrom, kharid.priceto , kharid.parvande FROM kharid INNER JOIN moshtari ON kharid.mid = moshtari.id where "+con;

                Qcommand.CommandText = commandText;
                Qcommand.CommandType = CommandType.Text;
                SqlCeDataAdapter a = new SqlCeDataAdapter();
                a.SelectCommand = Qcommand;
             a.Fill(k);
                Qconnection.Open();
                Qconnection.Close();
                return k;

            }
            catch (Exception ex)
            {

                throw new Exception(ex.Message);
                return k;
            }
        }

private void button1_Click(object sender, EventArgs e)
        {
            if (textBox3.Text == "" || textBox4.Text == "")
                MessageBox.Show("لطفا نام و نام خانوادگي را وارد نماييد");
            else
            {

                if (radioButton9.Checked == true)
                {
                    string u = "moshtari.name like '%'+@name+'%' and moshtari.lname like '%'+@lname+'%' ";
                   dataGridView1.DataSource= select(u);
                }
                else if (radioButton8.Checked == true)
                {
                    string u = "moshtari.name like '%'+@name+'%' and moshtari.lnamename like '%'+@lname+'%' and kharid.parvande=" + "'فعال'";
                    dataGridView1.DataSource = select(u);
                }
                else
                {
                    string u = "moshtari.name like '%'+@name+'%' and moshtari.lnamename like '%'+@lname+'%' and kharid.parvande!=" + "'فعال'";
                    dataGridView1.DataSource = select(u);
                }
            }
        }