數據庫中子類別的總和？

Question

我有一個類別和子類別字段的表。我想要在特定類別下的不同子類別的總和。像表

Category | Sub category | Amount 
----------+--------------+-------- 
Children | Cloth  | 200 
Children | Cloth  | 500 
Transport | Fuel  | 300 
Children | School  | 500 

我想要佈下的兒童類別的總和。就像那個不同的類別一樣。請幫助。

Answer 1

這是從你的問題不清楚你想要什麼，但我認爲這是下列之一：

它你想每的子類每類別，這樣做：如果你想只是 「兒童」 的子類別

select 
    category, 
    sub_category, 
    sum(amount) as total 
from mytable 
group by category, sub_category 

，這樣做：

select 
    sub_category, 
    sum(amount) as total 
from mytable 
group by sub_category 
where category = 'Children' 

Answer 2

是否這樣？

SELECT 
    sub_category 
    ,sum(amount) 
FROM 
    the_table 
GROUP BY 
    sub_category 
WHERE 
    category = 'Children'; 

或

SELECT 
    category 
    ,sub_category 
    ,sum(amount) 
FROM 
    the_table 
GROUP BY 
    category 
    ,sub_category 

---

測試/演示了使用SQLite：

$ sqlite3 test.sqlite 
SQLite version 3.7.15.2 2013-01-09 11:53:05 
Enter ".help" for instructions 
Enter SQL statements terminated with a ";" 
sqlite> create table t (category varchar, subcategory varchar, amount int); 
sqlite> insert into t values ('children', 'cloth', 200), ('children', 'cloth', 500), ('transport', 'fuel', 300), ('children', 'school', 500); 
sqlite> select * from t ; 
children|cloth|200 
children|cloth|500 
transport|fuel|300 
children|school|500 
sqlite> 
sqlite> select category, subcategory, sum(amount) from t group by category, subcategory; 
children|cloth|700 
children|school|500 
transport|fuel|300 
sqlite> 

Answer 3

select 
    category, 
    sub_category, 
    sum(amount) as total 
from mytable where sub_category = 'Cloth' 
group by category, sub_category