更改另一个表中的同一列时如何更新列？（postgresql）

Question

我需要一个函数或触发器来解决这个问题？？

customer_details :::

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

余额金额 :::

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

一旦我将pay_the_loan table 中的status 列更新为ok 以获取特定的creditid，即，

（更新 pay_the_loan set status='ok' where creditid=2）

then 它应该是 deduct balance_amount 表中 balance 列中的金额，并且应该更新它，即 balance_amount 表中的 (1000-600=400 where balance_amount.credit_type=fruits 和creditid=2 来自余额金额表）

可以给我发Function 或Trigger 来解决这个问题吗？

Answer 1

您最好稍微重组一下，创建一个包含原始贷款的loan_amount 表，然后创建一个显示当前余额并扣除所有付款的balance_amount 视图。这样，例如，更正付款金额不会使您的系统显示错误的余额。

为您计算当前余额的视图可能类似于：

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

您可以在同一个查询中更新两个表：

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。我已阅读 the documentation 的 postgresql update 语句。显然，我错了，不可能在一个查询中更新两个表。但是，我仍然认为您在这里不需要触发器。只需一个接一个地使用两个更新查询：

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';