SQL Case語句的邏輯是現有的邏輯

Question

比方說，我有一個數據集如下一個子集：

+----------+-------+----------+ 
| Customer | Price | Order ID | 
+----------+-------+----------+ 
| john  | 4  | 1  | 
| john  | 7  | 2  | 
| mike  | 12 | 3  | 
| mike  | 3  | 4  | 
| stacy | 3  | 5  | 
| stacy | 8  | 6  | 
+----------+-------+----------+ 

我想創建一個報告，讓2組，其價格的總和，一個GROUP A [john + mike + stacy]，另一個是B組[約翰+麥克]。
當我嘗試在SQL語句中編寫案例邏輯時發生問題。
由於組B是基團A的一個子集，它之前的情況下語句退出達到用於GROUP B. 邏輯說我使用此代碼：

with grouped_prices as (
select 
case when customer in ('john', 'mike', 'stacy') then 'GROUP A' 
when customer in ('john', 'mike') then 'GROUP B' 
else null end as customer_groups 
, price 
from mytable 
) 
select 
customer_groups 
, sum(price) as total 
from grouped_prices 
group by customer_groups 

這產生的結果

+-----------------+-------+ 
| customer_groups | total | 
+-----------------+-------+ 
| GROUP A   | 37 | 
+-----------------+-------+ 

但我想要的是

+-----------------+-------+ 
| customer_groups | total | 
+-----------------+-------+ 
| GROUP A   | 37 | 
+-----------------+-------+ 
| GROUP B   | 26 | 
+-----------------+-------+ 

我可以實現此解決方案使用UNION ALL語句，但我必須掃描表兩次，然後這是不高效的。有沒有比UNION ALL更聰明的解決方案，我沒有看到？

Answer 1

更新回答

你可以加入到被動態創建如下派生表：

select sum(cp.Price) as Total, t.Group 
from CustomerPrices cp 
join 
    (select 'Joe' as Customer, 'Group A' as Group 
    union all 
    select 'Sam' as Customer, 'Group A' as Group 
    union all 
    select 'John' as Customer, 'Group A' as Group 
    union all 
    select 'Joe' as Customer, 'Group B' as Group 
    union all 
    select 'John' as Customer, 'Group B' as Group) as t on t.Customer = cp.Customer 
group by t.Group