Since, only ID numbers are to be given by the user, I think a text box can be used to enter the ID with comma separation and then
string Ids = " cmpsno= '" + System.Text.RegularExpressions.Regex.Replace(TextBox1.Text.Trim(),@"\s*,\s*","' OR cmpsno= '") + "'";
string Ids = " cmpsno= " + System.Text.RegularExpressions.Regex.Replace(TextBox1.Text.Trim(),@"\s*,\s*"," OR cmpsno= ");
"SELECT conno,cmpsno,ctrx,dsysdate,cstnno,corigin FROM BRDATA WHERE conno = '" + richTextBox1.Text + "'OR cmpsno = '" + richTextBox1.Text + "'"
"SELECT conno,cmpsno,ctrx,dsysdate,cstnno,corigin FROM BRDATA WHERE " + Ids