Postgres触发功能 [英] Postgres trigger function

问题描述

我需要Postgres触发器方面的帮助。

I need help in Postgres triggers.

我的表格有两列：

sold boolean;
id_shop int;

它存储是否出售商品，或商店位于哪个商店。

It stores if item is sold, or at which shop its located at.

我需要一个触发器，如果​​将卖出更改为true，那么它也会将 id_shop 更改为 NULL （如果出售则不能在商店中购买……）

I need a trigger, if I change the "sold" to true, then it also changes the id_shop to NULL (It can't be in shop if sold...)

我尝试了不同的方法，但它不起作用或给出更新cmd时出错...

I tried different ways, but it doesn't work or gives an error on update cmd...

create or replace function pardota_masina_veikals() RETURNS trigger AS $pardota_masina$
begin
  IF NEW.sold=true THEN
    update masinas
      SET id_shop=null WHERE id=NEW.id;
  END IF;
  RETURN NEW;
END;
$pardota_masina$ LANGUAGE plpgsql;


CREATE TRIGGER pardota_masina_nevar_but_veikala 
    AFTER INSERT OR UPDATE ON masinas FOR EACH ROW EXECUTE PROCEDURE pardota_masina_veikals();

推荐答案

首先，您需要之前如果要更改要更新（或插入）的行的值，则会触发

First of all you need a before trigger if you want to change a value of the row being updated (or inserted)

第二，您无需更新表，只需分配将新值添加到NEW行：

Secondly you don't need to "update" the table, just assign the new value to the NEW row:

create or replace function pardota_masina_veikals() 
RETURNS trigger 
AS 
$pardota_masina$
begin
  IF NEW.sold=true THEN
    NEW.id_shop = NULL;
 END IF;
RETURN NEW;
END;
$pardota_masina$ 
LANGUAGE plpgsql;

CREATE TRIGGER pardota_masina_nevar_but_veikala 
   BEFORE INSERT OR UPDATE ON masinas 
   FOR EACH ROW EXECUTE PROCEDURE pardota_masina_veikals();

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