查找表中特定組值的總和

Question

我在MySQL中有兩個表。第一個是目錄，其中一列作爲類別，另一個表格以SP和CP作爲列。我想找到每個類別的總利潤。

我無法想出適當的查詢。我嘗試的每個查詢都會給出錯誤。誰能幫忙？

select A.Category,sum(B.SP group by A.Category) as TotalSP,sum(B.CP group by A.Category) as TotalCP, 
case 
when TotalSP>TotalCP then ((TotalSP-TotalCP)/TotalSP)*100 
when TotalSP<TotalCP then ((TotalSP-TotalCP)/TotalCP)*100 
end 
as TotalProfit 
from Catalog A,Stock B; 

注：負利潤自動被視爲損失。

Answer 1

select A.Category,sum(B.SP) as TotalSP,sum(B.CP) as TotalCP, 
case 
when TotalSP>TotalCP then ((TotalSP-TotalCP)/TotalSP)*100 
when TotalSP<TotalCP then ((TotalSP-TotalCP)/TotalCP)*100 
end 
as TotalProfit 
from Catalog A 
INNER JOIN Stock B ON B.catalog_id = A.id/*Write how your tables linked here*/ 
group by A.Category; 

此查詢選擇所有目錄記錄，連接各組股票的數據，然後組結果進行分類，計數總和。