PostgreSQL的：我怎樣才能得到所需的輸出低於

Question

描述我有一個表命名爲Box：

盒包含以下項目：

1. pen 

2. pencil 

3. scale 

4. eraser 

5. sharpener 

實際的表結構如下：

No  Item  quantity  bought_date 
_______________________________________________ 

1.  pen    3  14-12-2016 

2.  pencil    10  15-12-2016 

3.  pen    5  16-12-2016 

4.  eraser    7  16-12-2016 

5. sharpener    6  17-12-2016 

6.  pencil    3  18-12-2016 

7.  pen    3  18-12-2016 

需要輸出：

Item   Total_quantity 
___________________________ 

Pencil     13 

Pen      11 

Eraser     7 

Sharpener     6 

Scale      0 
___________________________ 

total     37 

請幫我這個查詢...

Answer 1

你可以這樣做：

SELECT t.item,sum(cast(coalese(b.quantity,'0') as integer)) as total_quantity FROM (
    SELECT 'pen' as item 
    UNION 
    SELECT 'pencil' as item 
    UNION 
    SELECT 'scale' as item 
    UNION 
    SELECT 'eraser' as item 
    UNION 
    SELECT 'sharpener' as item) t 
LEFT OUTER JOIN box b 
ON(t.item = b.item) 
GROUP BY t.item 
UNION 
(SELECT 'total',sum(quantity) 
FROM box) 

我根據您的意見調整了代碼，我認爲這是你想要的。

Answer 2

select it, sum(s) s from 
(
select b.item it, sum(b.qty::integer) s from box b group by b.item 
union 
select 'total' as item ,sum(qty::integer)total from box group by item 
) as un group by un.it; 

Answer 3

更短，更方便的方法是：

with items(item_no, item_name) as (
    values 
    (1, 'pen'), 
    (2, 'pencil'), 
    (3, 'scale'), 
    (4, 'eraser'), 
    (5, 'sharpener') 
) 
select 
    items.item_name, 
    coalesce(sum(box.quantity::int), 0) as total_quantity 
from 
    items 
    left join box on (box.item = items.item_name) 
group by 
    items.item_name 

union all 

select 
    'total', 
    coalesce(sum(box.quantity::int), 0) 
from 
    box