如何在 codeigniter 上使用 select as 进行多个联合？

Question

我正在尝试将以下代码转换为 php codeigniter 查询，但我似乎失败了。

此 SQL 完美运行：

SELECT item_stocks_1 as item_stocks_1 FROM orders WHERE item_id_1 = 7 AND delivery_date = '2019-03-24'
UNION
SELECT item_stocks_2 as item_stocks_2 FROM orders WHERE item_id_2 = 7 AND delivery_date = '2019-03-24'
UNION
SELECT item_stocks_3 as item_stocks_3 FROM orders WHERE item_id_3 = 7 AND delivery_date = '2019-03-24'
UNION
SELECT item_stocks_4 as item_stocks_4 FROM orders WHERE item_id_4 = 7 AND delivery_date = '2019-03-24'
UNION
SELECT item_stocks_5 as item_stocks_5 FROM orders WHERE item_id_5 = 7 AND delivery_date = '2019-03-24'

但是当我将它转换成这样的codeigniter查询时：

for($i=1;$i<$5;$i++){
$this->db->select('item_stocks_'.$i as 'item_stocks_'.$i);
$this->db->from('orders');
$this->db->where('item_id_', $filtered_item_id);
$this->db->where('delivery_date', '2019-03-24');
UNION
}

它总是失败。我曾尝试在 codeigniter 上搜索 unions，但它们只能合并 2 个表。

这就是我的桌子的样子：

delivery_date  |   item_id_1   |   item_stocks_1  |  item_id_2   |   item_stocks_2  | item_id_3   |   item_stocks_3  | item_id_4   |   item_stocks_4  | item_id_5   |   item_stocks_5  | 

Answer 1

使用组开始。

$this->db->select('item_stocks_'.$i as 'item_stocks_'.$i);
$this->db->from('orders');
for($i=1;$i<$5;$i++){
$this->db->or_group_start();
$this->db->where('item_id_', $filtered_item_id);
$this->db->where('delivery_date', '2019-03-24')->group_end();
}
$this->db->get();