MySQL UNION 似乎不能正常工作

Question

我有一个 SQL 查询用于从订单数据库中提取数据。我正在查询 2 tables 并使用 UNION ALL 合并结果。但是，UNION ALL 似乎没有按预期工作。这是我正在使用的查询：

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

这是我从查询中得到的：

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

但这就是我想要得到的：

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

谁能告诉我我做错了什么？？？

备注： oc_order table 的 date_added 列是日期时间，而 oc_return_custom 的 date_added 列只是文本。

Answer 1

UNION ALL 简单地将 单独的 GROUP BY 操作产生的两个数据集放在一起。

要获得预期的结果集，您必须将查询包装在子查询中并应用额外的 GROUP BY:

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

MySQL UNION 似乎不能正常工作

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