if( !in_array($sel_field, array('od_id', 'it_id', 'mb_id', 'od_name', 'od_tel', 'od_hp', 'od_b_name', 'od_b_tel', 'od_b_hp', 'od_deposit_name', 'od_invoice')) ){   //검색할 필드 대상이 아니면 값을 제거
    $sel_field = '';
}

--------------------------------------------------------------------------------------------------------------

$sql_search = "";
if ($search != "") {
    if($sel_field=='it_id'){
        $where[] = "  od_id in ( select distinct od_id  from {$g5['g5_shop_cart_table']} where it_id = '{$search}' and ct_status <> '쇼핑') ";
    }elseif ($sel_field != "") {
        $where[] = " $sel_field like '%$search%' ";
    }

    if ($save_search != $search) {
        $page = 1;
    }
}

--------------------------------------------------------------------------------------------------------------

<label for="sel_field" class="sound_only">검색대상</label>
<select name="sel_field" id="sel_field">
    <option value="od_id" <?php echo get_selected($sel_field, 'od_id'); ?>>주문번호</option>
    <option value="it_id" <?php echo get_selected($sel_field, 'it_id'); ?>>상품코드</option>
    <option value="mb_id" <?php echo get_selected($sel_field, 'mb_id'); ?>>회원 ID</option>
    <option value="od_name" <?php echo get_selected($sel_field, 'od_name'); ?>>주문자</option>
    <option value="od_tel" <?php echo get_selected($sel_field, 'od_tel'); ?>>주문자전화</option>
    <option value="od_hp" <?php echo get_selected($sel_field, 'od_hp'); ?>>주문자핸드폰</option>
    <option value="od_b_name" <?php echo get_selected($sel_field, 'od_b_name'); ?>>받는분</option>
    <option value="od_b_tel" <?php echo get_selected($sel_field, 'od_b_tel'); ?>>받는분전화</option>
    <option value="od_b_hp" <?php echo get_selected($sel_field, 'od_b_hp'); ?>>받는분핸드폰</option>
    <option value="od_deposit_name" <?php echo get_selected($sel_field, 'od_deposit_name'); ?>>입금자</option>
    <option value="od_invoice" <?php echo get_selected($sel_field, 'od_invoice'); ?>>운송장번호</option>
</select>
 

위에 중 붉게 강조된 부분 찾아서 추가해보시기 바랍니다.

근데 이게 상품이나 주문이 많아지면 좀 느려질 수 있습니다. ^^