MySQL UNION似乎沒有正常工作

Question

我有一個SQL查詢，我用來從訂單數據庫中提取數據。我在查詢2個表格，並使用UNION ALL結合結果。但是，UNION ALL似乎沒有按預期工作。下面是我使用的查詢：

SELECT year(oc_order.date_added) AS year, COUNT(oc_order.order_id) as cnt, SUM(ifnull(oc_order.new_total,oc_order.total)) as total 
FROM oc_order 
WHERE oc_order.order_status_id IN (1,3,5) 
    AND MONTH(oc_order.date_added) BETWEEN '01' AND '02' 
    AND DAY(oc_order.date_added) BETWEEN '01' AND '31' 
GROUP BY year(oc_order.date_added) 

UNION ALL 

SELECT ifnull(year(str_to_date(oc_return_custom.date_added,'%d-%m-%Y %H:%i:%s')),year(str_to_date(oc_return_custom.date_added,'%Y-%m-%d %H:%i:%s'))) AS year, COUNT(oc_return_custom.return_id) as cnt, SUM(oc_return_custom.total) as total 
FROM oc_return_custom 
WHERE ifnull(MONTH(str_to_date(oc_return_custom.date_added,'%d-%m-%Y %H:%i:%s')),MONTH(str_to_date(oc_return_custom.date_added,'%Y-%m-%d %H:%i:%s'))) BETWEEN '01' AND '02' 
    AND ifnull(DAY(str_to_date(oc_return_custom.date_added,'%d-%m-%Y %H:%i:%s')),DAY(str_to_date(oc_return_custom.date_added,'%Y-%m-%d %H:%i:%s'))) BETWEEN '01' AND '31' 
GROUP BY ifnull(year(str_to_date(oc_return_custom.date_added,'%d-%m-%Y %H:%i:%s')),year(str_to_date(oc_return_custom.date_added,'%Y-%m-%d %H:%i:%s'))) 
ORDER BY year DESC 

這是我從查詢得到：

+=======+========+=======+ 
| year | cnt | total | 
+=======+========+=======+ 
| 2016 | 200 | 1000 | 
| 2016 | 50 | 200 | 
| 2015 | 100 | 800 | 
| 2015 | 10 | 50 | 
+=======+========+=======+ 

，但是這是我希望得到：

+=======+========+=======+ 
| year | cnt | total | 
+=======+========+=======+ 
| 2016 | 250 | 1200 | 
| 2015 | 110 | 850 | 
+=======+========+=======+ 

誰能告訴我，我我做錯了什麼？

備註： oc_order表的date_added列是datetime，而oc_return_custom的date_added列只是文本。

Answer 1

UNION ALL只是把兩個數據集放在一起生成單獨的GROUP BY操作。

要獲得預期的結果集，你必須包裝在一個子查詢的查詢和應用附加GROUP BY：

SELECT year, SUM(cnt) AS cnt, SUM(total) AS total 
FROM (... your query here ...) AS t 
GROUP BY year