Question

I’ve a very simple database with following schema:

video (id, title, description)
category (id, name)
tag (id, name)

video_category_reference (video_id, category_id)
video_tag_reference(video_id, tag_id)

abc_table (video_id, description, categories)

The first five tables use InnoDB engine.

The last table – abc_table uses MyISAM engine and it contains some kind of “cache”. description column stores the result of CONCAT(video.title, video.description, GROUP_CONCAT(tag.name)) and categories column stores the result of GROUP_CONCAT(category.id).

What I need is a trigger that will populate abc_table after a new video is created. A new video will be created always the same way:

START TRANSACTION;

INSERT INTO video VALUES(NULL, "My video", "description");

SET @vid = (SELECT LAST_INSERT_ID());

INSERT INTO video_category_reference VALUES (@vid, 1), (@vid, 2), (@vid, 3), (@vid, 4);
INSERT INTO video_tag_reference VALUES (@vid, 5), (@vid, 6), (@vid, 7), (@vid, 8);

COMMIT;

Unfortunately I can’t use this trigger:

CREATE TRIGGER after_insert_on_video AFTER INSERT ON video FOR EACH ROW BEGIN
    SET @categories = (SELECT GROUP_CONCAT(category_id) FROM video_category_reference WHERE video_id = NEW.id GROUP BY video_id);
    SET @tags = (SELECT GROUP_CONCAT(t.name) FROM video_tag_reference vtr JOIN tag t ON vtr.tag_id = t.id WHERE video_id = NEW.id GROUP BY video_id);

    INSERT INTO video_search_table VALUES (NEW.id, CONCAT(NEW.title, NEW.raw_description, @tags), @categories);
END$$

…as it will be executed before inserts on *_reference tables will be done.

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Is there any way I could force MySQL to execute a trigger after the transaction is commited? Or do I have to create triggers for *_referemce tables that will modify values in abc_table?

Answer 1

You could change your trigger to AFTER UPDATE and have a quick:

UPDATE video SET id=@vid WHERE id=@vid;

to trigger the trigger before the transaction ends. Bonus: if your video information is updated, the trigger runs again =D.