mysql - 添加三个子查询的结果

Question

我有这张表:

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

我尝试过这个:

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

当只能有一列时，您在子查询中选择了两列。

这样的东西会给你你正在寻找的东西:

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;