如何更改另一個表中的同一列時更改列（postgresql）

Question

我需要一個函數或觸發器來解決這個問題？

customer_details :::

custid name creditid 
---------------------------- 
    2  a  1 
    3  b  2 
    4  c  3 

BALANCE_AMOUNT :::

creditid credit_type balance 
----------------------------------- 
    1   rent  1000 
    1   transport 2000 
    1   food  1000 
    1   fruits  1500 
    2   rent  1500 
    2   transport 1020 
    2   food  1200 
    2   fruits  1000 
    3   transport 1600 
    3   rent  2000 
    3   food  1540 
    3   fruits  1560 

Pay_the_loan :::

creditid credit_type  Pay  status 
--------------------------------------------- 
    1   rent   500  null 
    2   fruits   600  null 
    3   transport  400  null 
    1   fruits   500  null 

一旦我在pay_the_loan table的status柱更新爲ok用於特定creditid i .E ..，

（更新pay_the_loan設置狀態= 'OK'，其中creditid = 2）

then應該deduct在BALANCE_AMOUNT表從balance柱的量和它應該被更新，即，（1000-600 = 400在BALANCE_AMOUNT表where balance_amount.credit_type =水果和creditid = 2從平衡量表）

可能交我Function或Trigger來解決這個親呃？

Answer 1

您可能會更好地重組一點，創建loan_amount表與原始貸款，只是使balance_amount視圖顯示當前餘額與扣除所有支付。這樣，例如，支付金額的更正不會導致您的系統顯示錯誤的餘額。

爲您計算當前餘額的視圖可能類似於;

CREATE VIEW balance_amount AS 
    SELECT la.creditid, la.credit_type, amount 
       - COALESCE(SUM(pay),0) balance 
    FROM loan_amount la 
    LEFT JOIN pay_the_loan pl 
     ON la.creditid = pl.creditid 
    AND la.credit_type = pl.credit_type 
    AND pl.status = 'OK' 
    GROUP BY la.creditid, la.credit_type, la.amount; 

An SQLfiddle with the whole setup。

Answer 2

您可以更新在同一查詢兩個表：

update 
    pay_the_loan 
set 
    pay_the_loan.status='ok', 
    balance_amount.balance=balance_amount.balance-pay_the_loan.Pay 
from balance_amount 
where 
    pay_the_loan.creditid=balance_amount.creditid 
    and 
    pay_the_loan.creditid=2 
    and 
    balance_amount.credit_type='fruits'; 

更新。我已閱讀postgresql update聲明的the documentation。顯然，我錯了，並且無法在單個查詢中更新兩個表。不過，我仍然認爲你不需要觸發這裏。只需使用兩個更新查詢：

update 
    pay_the_loan 
set 
    status='ok' 
where 
    pay_the_loan.creditid=2; 

update 
    balance_amount 
set 
    amount=balance_amount.amount-pay_the_loan.Pay 
from pay_the_loan 
where 
    pay_the_loan.creditid=balance_amount.creditid 
    and 
    pay_the_loan.creditid=2 
    and 
    balance_amount.credit_type='fruits';