Postgresql SUM和UPDATE

Question

我想問一下SUM，然後在Postgresql DB中更新它。
在我的情況下，我想總結（單位）在stockdary表中，然後做與表產品（stockvolume）的扣除/減去。

我能總結在表stockdiary單位：

 SELECT NAME,SUM(UNITS) AS MINUS 
    FROM STOCKDIARY 
    INNER JOIN PRODUCTS 
    ON PRODUCTS.ID = STOCKDIARY.PRODUCT 
    GROUP BY NAME 

    result => 
    name    || minus 
    USB CABLE 1M  || -8 
    USB CHARGER  || -3 

那麼問題是如何減去減去和stockvolume和更新回到產品表？

stockdiary表
ID（PK），datenew，產品，單位價格

產品表
姓名，身份證（PK），pricebuy，pricesell，stockvolume

@感謝Vivek.S它作品。

UPDATE products 
    SET stockvolume = sub.minus 
    FROM (SELECT 
    SUM(UNITS) AS MINUS,PRODUCTS.ID 
    FROM STOCKDIARY 
    INNER JOIN PRODUCTS ON PRODUCTS.ID = STOCKDIARY.PRODUCT 
    GROUP BY NAME) sub 
    WHERE sub.productid = products.productid 

Answer 1

update products set stockvolume = stockvolume - diary.minus from 
(SELECT STOCKDIARY.product,SUM(UNITS) AS MINUS 
FROM STOCKDIARY 
INNER JOIN PRODUCTS 
ON PRODUCTS.ID = STOCKDIARY.PRODUCT 
GROUP BY STOCKDIARY.product) as diary where products.id= diary.product 

不使用保留字作爲表名，字段名等.. :)