SQL查询按总和排序答案

【问题标题】：SQL query to order by sum of sumsSQL查询按总和排序
【发布时间】：2021-03-30 07:02:46
【问题描述】：

提前感谢您的帮助。

解释我的问题最简单的方法可能是用一个例子，所以我建立了一个沙盒数据库，有两个表和以下内容：

类别：

 supercategory | category
---------------+----------
 fruit         | apple
 fruit         | orange
 fruit         | banana
 vegetable     | carrot
 vegetable     | onion
 vegetable     | celery
 grain         | rice
 grain         | wheat
 grain         | barley

篮子：

 category | amount
----------+--------
 apple    |      2
 carrot   |      4
 wheat    |      1
 orange   |      5
 celery   |      4
 orange   |      3
 barley   |      2
 barley   |      5
 apple    |      1
 carrot   |      2
 rice     |      5
 wheat    |      3
 onion    |      2

我要做的是查询每个类别的总和，如下所示：

SELECT 
    categories.superCategory, baskets.category, 
    SUM(baskets.amount::numeric) AS categorySum
FROM
    baskets 
LEFT OUTER JOIN 
    categories ON categories.category = baskets.category
GROUP BY 
    categories.superCategory, baskets.category
ORDER BY 
    superCategory;

 category | supercategory | categorysum
----------+---------------+-------------
 apple    | fruit         |           3
 orange   | fruit         |           8
 barley   | grain         |           7
 rice     | grain         |           5
 wheat    | grain         |           4
 carrot   | vegetable     |           6
 celery   | vegetable     |           4
 onion    | vegetable     |           2

结果表正是我想要的，除了排序。我想按总和对每个超类别进行排序，然后在每个超类别中按总和对每个类别进行排序。所以我想要这张桌子的顺序是：


barley | grain     | 7      <---- The total for the "grain" supercategory is 16, so put it first
rice   | grain     | 5
wheat  | grain     | 4
carrot | vegetable | 6      <---- The total for vegetables is 12
celery | vegetable | 4
onion  | vegetable | 2
orange | fruit     | 8      <---- The total for fruits is 11
apple  | fruit     | 3

我对 SQL 的经验不足，不知道如何最好地完成此任务。我尝试了一些嵌套的 SELECT 函数，但没有弄清楚如何让它正常工作，或者这是否是最好的方法。

【问题讨论】：

标签： sql postgresql sql-order-by aggregate-functions window-functions

【解决方案1】：

您可以使用ORDER BY 子句中的窗口函数SUM() 来做到这一点：

SELECT b.category, 
       c.superCategory, 
       SUM(b.amount::numeric) AS categorySum
FROM baskets b LEFT OUTER JOIN categories c
ON c.category = b.category
GROUP BY c.superCategory, b.category
ORDER BY SUM(SUM(b.amount::numeric)) OVER (PARTITION BY c.superCategory) DESC, 
         categorySum DESC;

请参阅demo。
结果：

> category | supercategory | categorysum
> :------- | :------------ | ----------:
> barley   | grain         |           7
> rice     | grain         |           5
> wheat    | grain         |           4
> carrot   | vegetable     |           6
> celery   | vegetable     |           4
> onion    | vegetable     |           2
> orange   | fruit         |           8
> apple    | fruit         |           3

【讨论】：

【解决方案2】：

你在找这个吗：

select superCategory, category , categorySum from (
SELECT 
    categories.superCategory, baskets.category, 
    SUM(baskets.amount) over ( partition by categories.superCategory,baskets.category) AS categorySum
FROM
    baskets 
LEFT OUTER JOIN 
    categories ON categories.category = baskets.category
) X
group by superCategory, category , categorySum
ORDER BY SUM(categorySum) over ( partition by superCategory) DESC,categorySum desc

【讨论】：

。 .子查询不是必需的。

【解决方案3】：

试试这个并使用JOIN和subquery：

SELECT T.category
     , T.superCategory
     , T.Sums AS categorySum
  FROM
       (
        SELECT categories.superCategory
             , baskets.category
             , SUM(baskets.amount) AS Sums
         FROM baskets
         JOIN categories ON categories.category = baskets.category
        GROUP BY categories.superCategory, baskets.category
      )T
 JOIN (
       SELECT categories.superCategory
            , SUM(baskets.amount) AS Sums
         FROM baskets
         JOIN categories ON categories.category = baskets.category
        GROUP BY categories.superCategory
      )TA ON T.superCategory = TA.superCategory
ORDER BY TA.Sums DESC, T.Sums DESC

查看这个sqlfiddle的结果

【讨论】：