Question

我有一列文件夹名称，我有一个部分目录地址。当我添加或更改文件夹名称时 - 我希望附加目录地址...

所以......当我更新文件夹名称时，触发器应该只是自动将文件夹名称添加到目录的末尾。但是，虽然我在MySQL中的工作相似 - 出于某种原因，我无法让SQLite工作

`CREATE TRIGGER df_match_a AFTER UPDATE ON user_cats
BEGIN
SET NEW.save_directory = CONCAT(OLD.save_directory,NEW.folder)
END;`

我得到了：

near "SET": syntax error:

这是一个可以实现我想要的MySQL代码... 它会自动更新API_Call＆gt;＆gt;当我将新信息添加到用户名 - 和Playlist_ID

时

CREATE DEFINER=`root`@`localhost` TRIGGER `api_links` BEFORE INSERT ON `spotify follow lists` FOR EACH ROW BEGIN
    SET NEW.`API Call` = CONCAT("https://api.spotify.com/v1/users/",NEW.`Username`,"/playlists/",NEW.`Playlist ID);
END

这就是数据库转储的样子......

PRAGMA foreign_keys=OFF;
BEGIN TRANSACTION;
CREATE TABLE IF NOT EXISTS "user_cats" (
    `category`  TEXT,
    `uploader`  TEXT,
    `folder`    TEXT,
    `playlists` TEXT,
    `playlist_image`    TEXT,
    `save_directory`    TEXT
);
INSERT INTO user_cats VALUES('Comics','ComicsExplained','DC Rebirth','[''New to DC Comics? Start here!'']',NULL,'%USERPROFILE%\Videos\Online Videos\Comics\ComicsExplained\');
INSERT INTO user_cats VALUES('Comics','Comicstorian',NULL,NULL,NULL,NULL);
INSERT INTO user_cats VALUES('Video Games','IGN','Daily Fix','[''Daily Fix'']',NULL,'%USERPROFILE%\Videos\Online Videos\Video Games\IGN\Daily Fix\');
INSERT INTO user_cats VALUES('Comics','Marvel Entertainment','Marvel Top 10','[''Marvel Top 10'']',NULL,'%USERPROFILE%\Videos\Online Videos\Comics\Marvel Entertainment\');
INSERT INTO user_cats VALUES('','ScrewAttack!',NULL,NULL,NULL,NULL);
COMMIT;

Answer 1

我认为它类似

CREATE TRIGGER df_match_a AFTER UPDATE ON user_cats BEGIN UPDATE user_cats SET NEW.save_directory = CONCAT(OLD.save_directory,NEW.folder) END;

Answer 2

感谢您的帮助;我终于明白了！以下是详细信息......

因此，MySQL执行和SQLite之间存在一些差异......

MySQL使用CONCAT()，但SQLite使用||

所以...这...

SET NEW.save_directory = CONCAT(OLD.save_directory,NEW.folder)

...成了

SET NEW.save_directory = (OLD.save_directory || NEW.folder)

我不需要添加新内容。声明

SET NEW.save_directory = (OLD.save_directory || NEW.folder)

是语法错误，但是......

SET save_directory = (OLD.save_directory || NEW.folder)

作品

触发器语句的结尾需要分号。

SET save_directory = (OLD.save_directory || NEW.folder) END;

但是，我应该在New.folder)

`SET save_directory = (OLD.save_directory || NEW.folder);
END;`

我需要WHERE选项才能使用新的save_directory名称

folder

有了......

SET save_directory = (OLD.save_directory || NEW.folder); END;

一个folder名称的更改将更改所有 save_directory行

但是，添加WHERE选项可确保只更新NEW.folder名称的行。

SET save_directory = (OLD.save_directory || NEW.folder) WHERE folder = NEW.folder; END

最后......

声明本身需要更改......

使用...

SET save_directory = (OLD.save_directory || "\" || NEW.folder) WHERE folder = NEW.folder;
END

我的旧save_directory每次都会附加新的。例如，我开始......

%USERPROFILE%\Videos\Online Videos\IGN

将文件夹更新为Daily Fix ...

%USERPROFILE%\Videos\Online Videos\Video Games\IGN\Daily Fix

将文件夹更新为Mass Effect ...

%USERPROFILE%\Videos\Online Videos\Video Games\IGN\Daily Fix\Mass Effect

等等......

但是，如果我使用了类别和上传者列......

UPDATE user_cats SET save_directory = ("%USERPROFILE%\Videos\Online Videos\" || category || "\" || uploader || "\" || NEW.folder) WHERE folder = NEW.folder;
END;

终于有效了！：）

另外，我在插入新值时做了第二个语句处理，而不仅仅是在我更新时。所以，最后的TRIGGER陈述是......

<强>解决方案：

CREATE TRIGGER df_match_a
AFTER UPDATE ON user_cats FOR EACH ROW
BEGIN
UPDATE user_cats SET save_directory = ("%USERPROFILE%\Videos\Online Videos\" || category || "\" || uploader || "\" || NEW.folder) WHERE folder = NEW.folder;
END;

CREATE TRIGGER df_match_b
AFTER INSERT ON user_cats FOR EACH ROW
BEGIN
UPDATE user_cats SET save_directory = ("%USERPROFILE%\Videos\Online Videos\" || category || "\" || uploader || "\" || NEW.folder) WHERE folder = NEW.folder;
END;

如何创建一个SQLite触发器，根据另一个条目更新条目？

2 个答案: