从SQL sever 2005中向listbox中添加数据表中的一列名字Name，但是名字不重复添加到listbox中，如下代码应该怎么修改？
           this.LstAll1.Items.Clear();
            SqlConnection conn = new SqlConnection("Data Source=WANGHUI\\SQLEXPRESS;Initial Catalog=DB_Hyg;Integrated Security=True");
            conn.Open();
            SqlCommand cmd = new SqlCommand("select *from Hydrochemistry", conn);
            SqlDataReader sdr = cmd.ExecuteReader();
            while (sdr.Read())
            {
                if (!this.LstAll1.Items .Contains("？"))

                {
                LstAll1.Items.Add(sdr["Name"].ToString().Trim());
                }
            }
            sdr.Close();
            conn.Close();

        private void frmPara_Load(object sender, EventArgs e)
        {
            this.LstAll1.Items.Clear();
            SqlConnection conn = new SqlConnection("Data Source=WANGHUI\\SQLEXPRESS;Initial Catalog=DB_Hyg;Integrated Security=True");
            conn.Open();
            SqlCommand cmd = new SqlCommand("SELECT  * FROM Hydrochemistry", conn);
            SqlDataReader sdr = cmd.ExecuteReader();
            while (sdr.Read())
            {
                if (!this.LstAll1.Items .Contains("?"))

                {
                LstAll1.Items.Add(sdr[" Name"].ToString().Trim());
                }
            }
            sdr.Close();
            conn.Close();
        }
我现在的问题是让Name这一列不重复的显示！