Postgresql SUM和UPDATE

Question

我想询问SUM然后在Postgresql DB中更新它。
在我的情况下，我想在stockdiary表中求和（单位），然后用表产品（stockvolume）进行扣除/减法。

我能够在库存表中对单位进行求和：

     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  

那么问题是如何减去减去和 stockvolume 并将其更新回产品表？

stockdiary表
 ID（PK），datenew，产品，单位，价格

产品表
 名称，ID（PK），pricebuy，pricesell，stockvolume

@ Vivek.S谢谢你的工作。

    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

不要使用保留字作为表名，列名等......：）