Postgres 添加列类别以根据特定列的总和查看

Question

我有 动物table table:

id	dog_amount	cat_amount	bird_amount
1	4	4	6
2	2	4	5
3	2	1	3

我想创建这样的视图：

id	animal	total
1	dogs	8
2	cats	9
3	birds	14

我怎样才能做到这一点？如何在视图中添加额外的列“动物”？

Answer 1

UNION ALL不同的动物，在派生table（即子查询。）GROUP BY其结果。

create view animalview as

select animal, SUM(total)
from
(
    select 'dogs' animal, dog_amount   as total   from animaltable
    UNION ALL 
    select 'cats' animal, cat_amount   as total   from animaltable
    UNION ALL
    select 'birds' animal, bird_amount as total   from animaltable
) dt
group by animal

Answer 2

另一种获得所需结果的方法，首先我在子查询（一行）中获取每只动物的总数，然后使用 LATERAL JOIN 和“常量 table”（使用 VALUES):

CREATE VIEW animals_view AS

SELECT s.*
FROM (SELECT SUM(dog_amount) AS dogs, SUM(cat_amount) AS cats, SUM(bird_amount) AS birds
      FROM animaltable) AS t
JOIN LATERAL (VALUES (1, 'dogs', t.dogs), (2, 'cats', t.cats), (3, 'birds', t.birds)) AS s(id, animal, total) ON TRUE;

Postgres 添加列类别以根据特定列的总和查看

Postgres add column category to view base on sum of specific column

sql

postgresql

sql-view