MySQL query date completion (continuous) method

SELECT
    od.date,
    od.orderCount
FROM
    (
        SELECT
            DATE_FORMAT(order_time,'%Y-%m-%d') date,
            count(*) orderCount
        FROM
            order
        WHERE
            order_time>'开始时间' and order_time<'结束时间'
        GROUP BY DATE_FORMAT(order_time,'%Y-%m-%d')

        UNION (SELECT 0, '2017-03-01')
        UNION (SELECT 0, '2017-03-02')
        UNION (SELECT 0, '2017-03-03')
        UNION (SELECT 0, '2017-03-04')
        UNION (SELECT 0, '2017-03-05')
        UNION (SELECT 0, '2017-03-06')
        UNION (SELECT 0, '2017-03-07')
        UNION (SELECT 0, '2017-03-08')
        -- 很多个UNION ......
    ) AS od
GROUP BY od.date
ORDER BY od.date ASC
如果有日期表那就用联表就行了，这里是不联表的方法，在程序上做处理后拼接到sql上 

public function getLaidianLaifang($proj_ids, $start_date, $end_date, $gjfs, $type){
if(empty($proj_ids)){
return [];
}
$where = " and proj_id in ('".implode("','", $proj_ids)."')";
$rs = $this->dealDate($type, $start_date, $end_date);
$group                             = $rs['group'];
$union = $rs['union'];
$sql = "select d.gj_cst_sum,d.date_type from (select count(DISTINCT opp_id) as gj_cst_sum,{$group} as date_type from s_opp2gjjl where gjfs = {$gjfs} and gj_date BETWEEN :start_date and :end_date {$where} GROUP BY {$group} {$union}) 
            as d GROUP BY d.date_type ORDER BY d.date_type ASC";
return             $this->kfsDb->createCommand($sql, [':start_date' => $start_date, ':end_date' => $end_date.' 23:59:59'])->queryAll();
}

/**
 * 处理时间，把缺的补上
 * */
private function dealDate($type, $start_date, $end_date, $proj = null){
$union = '';
$group = '';
if($type == 1){
$group = "HOUR(gj_date)";
for($i = 0; $i < 24; $i++){
$union .= " UNION (SELECT 0,                                        {$i} {$proj})";
}
    }elseif($type == 3){
$group = "DATE(gj_date)";
for($i = $start_date; $i <= $end_date; $i++){
$union .= " UNION (SELECT 0, '{$i}' {$proj})";
}
    }elseif ($type == 4){
                                                    $group = "WEEK(gj_date,0)";
$s = date('W',strtotime($start_date));
$e = date('W',strtotime($end_date));
for($i = $s; $i <= $e; $i++){
$union .= " UNION (SELECT 0,{$i} {$proj})";
}
    }elseif ($type == 5){
                                                    $group = "MONTH(gj_date)";
        $s = date('n',strtotime($start_date));
        $e = date('n',strtotime($end_date));
        for($i = $s; $i <= $e; $i++){
            $union .= " UNION (SELECT 0,{$i} {$proj})";
        }
    }
    return ['group' => $group, 'union' => $union];
}