SQL 查询按总和排序

Question

Thanks in advance for any help.

The easiest way to explain my question is probably with an example, so I set up a sandbox database with two tables and the following contents:

Categories :

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

Baskets :

 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

What I want to do is query the sum of each category, like this:

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;

Which returns:

 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

That resulting table is exactly what I want, except for the ordering. I'd like to order by each supercategory by sum, and then within each supercategory order each category by its sum. So the order I want this table in would be:

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

I'm not experienced enough about SQL to know how best to accomplish this. I had tried some nested SELECT functions, but wasn't figuring out how to get that to work right, or if that is even the best approach.

Answer 1

Are you looking for this:

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

Answer 2

You can do it with the window function SUM() in the ORDER BY clause:

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;

See the demo .
Results:

> 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

Answer 3

Try this and use JOIN and 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

See result in this sqlfiddle