创建 SQL 触发器以更新另一个表时出错

Posted 2023-05-09

【中文标题】创建 SQL 触发器以更新另一个表时出错

【英文标题】：Error when creating SQL trigger to update another table

【发布时间】：2021-09-21 03:22:31

【问题描述】：

我在“ON”处或附近得到语法错误，代码如下。写这个的正确方法是什么？我正在尝试为 game_info 表创建一个触发器，该触发器将在将数据添加到 game_info 时更新 game_count 表。

CREATE TRIGGER my_trigger
    ON game_info
    AFTER INSERT
AS
BEGIN
    INSERT INTO game_count(title,count)
    SELECT title, count(*)
    FROM public.game_info
    GROUP BY title
    ORDER BY count DESC
END

创建 game_info 表

CREATE TABLE game_info (
rental_id INT NOT NULL,
film_id SMALLINT NOT NULL,
title CHAR(255) NOT NULL,
description TEXT NOT NULL,
length SMALLINT NOT NULL
);

创建 game_count 表

CREATE TABLE game_count (
title CHAR(255) NOT NULL,
count BIGINT NOT NULL
)

将数据插入游戏信息

INSERT INTO game_info (rental_id, film_id, title, description, length)
SELECT
r.rental_id,
i.film_id,
f.title,
f.description,
f.length
FROM public.inventory as i
INNER JOIN public.rental as r ON r.inventory_id=i.inventory_id
INNER JOIN public.film as f ON f.film_id=i.film_id

将数据插入game_count

INSERT INTO game_count(title, count)
SELECT title, count(*)
FROM public.game_info
GROUP BY title
ORDER BY count DESC;

【问题讨论】：

将after insert 移到on game_info 上方，再试一次

@zedfoxus 它给了我错误消息“在“AS”或附近出现语法错误

删除 as 并重试。另外，请遵循以下教程：mysqltutorial.org/create-the-first-trigger-in-mysql.aspx 和 w3resource.com/mysql/mysql-triggers.php#MTAI

您的触发逻辑似乎有误。在当前状态下（在语法修复之后），它将为每个插入的行插入一堆新行到目标表中......也许您需要更新现有行中的数据（并在相应的游戏行不存在时插入新行） ?

【参考方案1】：

你可以试试：

DELIMITER $$
CREATE TRIGGER my_trigger AFTER INSERT ON game_info
FOR EACH ROW
BEGIN
    INSERT INTO game_count set title=new.title, count=(select count(*) from FROM game_info GROUP BY title) ;    
END$$
DELIMITER ;

trigger 甚至适用于game_info 表上的多个插入值。