populated filter data in combo box in C# windows application

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C#

Hi All
I am currently working on C# windows application where I am using MS Access 2003 DB as back end I am trying to get filter data in combo box as example If I put 0 so it should show all 0 started data in the combo box but it doesn't and also under which event of the combo box it will come below I show Code

private void comboBox_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
        
        {
            comboBox.Refresh();
            string str = "SELECT BookID FROM BookMaster WHERE BookID like '%" + comboBox.Text + "%'";
            OleDbCommand cmd = new OleDbCommand(str, conn);
            OleDbDataAdapter da = new OleDbDataAdapter();
            da.SelectCommand = cmd;
            DataTable dt = new DataTable();
            da.Fill(dt);           
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                comboBox.Items.Add(dt.Rows[i]["BookID"]);
            }            
        }  

but it is not coming as expectation

Thanks & Regards
Indrajit Dasgupta