case 语句和 group by 没有正确分组 (postgresql)

Question

当不应该对列进行分组时，如何获得正确的分组。查询得到错误结果

CREATE TABLE inv
    (invid int, co int4, type varchar(1), sum int4);
INSERT INTO inv
    (invid, co, type, sum)
VALUES
    (1, 1,'J',1000),
    (2, 1,'O',2000),
    (3, 2,'O',3000),
    (4, 3,'J',4000),
    (5, 4,'J',1000),
    (6, 2,'O',2000),
    (7, 1,'J',1000)
;

CREATE TABLE co
    (coid int, name varchar(30));
INSERT INTO co
    (coid, name)
VALUES
    (1,'Volvo'),
    (2,'BMW'),
    (3,'Microsoft'),
    (4,'Apple')
;

分组时使用 when 给出错误结果。

SELECT name,type,
CASE 
   WHEN type ='J' THEN 100
   WHEN type ='O' THEN 200
   ELSE 0 END AS cost,
sum(sum)
FROM inv
LEFT JOIN co ON coid=co
GROUP BY name,type

沃尔沃出现了两次，因为发票有两种类型。

Volvo     J  100  2000
Apple     J  100  1000
Microsoft J  100  4000
BMW       O  200  5000
Volvo     O  200  2000

问题很简单：如何只按公司分组？

我知道以前也有人问过类似的问题，但我找不到任何涉及的案例。

预期输出（不需要类型）：

Volvo       300  4000
Apple       100  1000
Microsoft   100  4000
BMW         200  5000

http://sqlfiddle.com/#!15/35c5df/5

TIA

Answer 1

select
    name,
    sum ( case
       when type = 'J' then 100
       when type = 'O' then 200
       else 0 end
    ) as cost,
    sum("sum") as "sum"
from inv left join co on coid=co
group by name

case 语句和 group by 没有正确分组 (postgresql)

case statement and group by not grouped correctly (postgresql)

postgresql

postgresql-9.1