如何实现更新 "status" 字段时填充的 "stolen_at" 字段？ TRIGGER 函数和 GENERATED ALWAYS AS 附加尝试

Question

如何更新 stolen_at 以便在 status 从 INSTOCK 更新到 STOLEN 时填充当前时间戳？

我已经尝试过基于触发器的方法，但它包含一个错误：

SQL Error [2F005]: ERROR: control reached end of trigger procedure without RETURN
  Where: PL/pgSQL function stolen()

触发方式：

CREATE TABLE items ( 
    id INTEGER PRIMARY KEY, 
    item_name text NOT NULL, 
    item_status text NOT NULL, 
    stolen_at TIMESTAMP WITHOUT TIME zone 
);


CREATE OR REPLACE FUNCTION stolen() RETURNS TRIGGER AS $CODE$ 
BEGIN
   -- Populate stolen_at with datetime only if item_status 
   -- changes from INSTOCK to STOLEN
   IF NEW.item_status = 'STOLEN' 
   AND OLD.item_status = 'INSTOCK' 
   THEN
      NEW.stolen_at : = now() AT TIME zone 'utc';
   END IF;
END $CODE$ LANGUAGE plpgsql;


CREATE TRIGGER populate_stoken 
AFTER INSERT OR UPDATE OF item_status 
ON items FOR EACH ROW EXECUTE PROCEDURE stolen();

探索的另一种方法是接受 id 和 new_item_status 并填充 item_status 字段的函数。虽然我无法让它工作：

CREATE TABLE items ( 
    id INTEGER PRIMARY KEY, 
    item_name text NOT NULL, 
    item_status text NOT NULL, 
    stolen_at TIMESTAMP WITHOUT TIME zone NOT NULL GENERATED ALWAYS AS (stolen2(id, item_status)) STORED 
);

CREATE OR REPLACE FUNCTION stolen2(id INT, new_item_status text) RETURNS TIMESTAMP AS $CODE$ 
DECLARE stolen_at TIMESTAMP WITHOUT TIME zone;
BEGIN
   SELECT
      * 
   FROM
      items 
   WHERE
      id = id 
      AND item_status = 'INSTOCK';      
      
   -- Return if conditions satisfy otherwise return null 
   IF found AND new_item_status = 'STOLEN' 
   THEN
      RETURN now() AT TIME zone 'utc';
   ELSE
      RETURN NULL;
END IF;
END $CODE$ LANGUAGE plpgsql;

这两种方法中哪一种是首选（例如，资源密集度较低）以及实施它们的正确方法是什么？

Answer 1

您的第一个触发器几乎没问题，但有两处错误：

它必须是一个 BEFORE 触发器，以便您可以修改新行
您在决赛 END; 之前错过了 RETURN NEW;（有关讨论，请参阅 here）

如何实现更新 "status" 字段时填充的 "stolen_at" 字段？ TRIGGER 函数和 GENERATED ALWAYS AS 附加尝试

How to acheive a "stolen_at" field which is populated when the "status" field is updated? TRIGGER function and GENERATED ALWAYS AS attempts attached

postgresql

triggers

plpgsql

postgresql-triggers