添加三个子查询的结果

Question

我有这张桌子：

id   item_name_1   quantity 1   item_name_2   quantity_2   item_name_3   quantity_3
-----------------------------------------------------------------------------------
1    Apple         2            Pear          3            Orange        5
2    Pear          1            Apple         4
3    Orange        6
4    Apple         1            Pear          2            Orange        3

我想要这个结果：

item     total
--------------
Apple    7
Pear     6
Orange   14

我试过了：

SELECT

(SELECT item_name_1, SUM(quantity_1) AS count FROM table1
GROUP BY item_name_1) AS item,

(SELECT item_name_2, SUM(quantity_2) AS count FROM table1
GROUP BY item_name_2) AS item,

(SELECT item_name_3, SUM(quantity_3) AS count FROM table1
GROUP BY item_name_3) AS item,

SUM(count) AS total
FROM table1
GROUP BY item;

错误代码：1241。操作数应包含1列

有什么建议吗？

Answer 1

我会这样试试。

select t.item_name_1, s1+s2+s3

from
(
select * From
(    
select sum(quantity_1) as s1, item_name_1
from
table1
group by item_name_1
) t1

full outer join 

(    
select sum(quantity_2) as s2, item_name_2
from
table1
group by item_name_2
) t2 on t1.item_name_1 = t2.item_name_2

full outer join 

(    
select sum(quantity_3) as s3, item_name_3
from
table1
group by item_name_3
) t3 on t2.item_name_2 = t3.item_name_3

) t

Answer 2

当只有一列时，您在子查询中选择了两列。

这样的东西会让你得到你想要的东西：

SELECT item_name, SUM(quantity) AS quantity
FROM
(SELECT item_name_1 AS item_name, SUM(quantity_1) AS quantity
FROM table1
GROUP BY item_name_1

UNION ALL

SELECT item_name_2 AS item_name, SUM(quantity_2) AS quantity
FROM table1
GROUP BY item_name_2

UNION ALL

SELECT item_name_3 AS item_name, SUM(quantity_3) AS quantity
FROM table1
GROUP BY item_name_3) AS ABB1
GROUP BY item_name;