Mysql trigger to update empty field with condition - mysql

Question

I have a MySQL table , look like this
t id lang title
1 7 en_UK my_title
1 7 kh_KH
I want write a trigger that update title to my_title with the same id is 7
Result
t id lang title
1 7 en_UK my_title
1 7 kh_KH my_title
From my understanding.
DELIMITER $$
CREATE TRIGGER upd_title BEFORE UPDATE ON `term`
FOR EACH ROW BEGIN
IF (NEW.title IS NULL OR NEW.title= '') THEN
SET NEW.title= ??? ;
END IF;
END$$
DELIMITER ;
[UPDATE1]->not works (trigger not being created)
DELIMITER $$
DROP TRIGGER IF EXISTS `update_category_after_insert`
CREATE TRIGGER `update_category` AFTER INSERT ON `categories`
FOR EACH ROW BEGIN
DECLARE loc_title text;
IF (NEW.libelle_categorie IS NULL OR NEW.libelle_categorie= '') THEN
select libelle_categorie into loc_title from categories where NEW.num_noeud= num_noeud and langue = 'en_UK';
SET NEW.libelle_categorie = loc_title;
END IF;
END
DELIMITER ;
[UPDATE2]
DELIMITER $$
CREATE TRIGGER ``update_category_after_insert`` BEFORE INSERT ON `categories`
FOR EACH ROW BEGIN
DECLARE loc_title text;
IF (NEW.libelle_categorie IS NULL OR NEW.libelle_categorie= '') THEN
select libelle_categorie into loc_title from categories where NEW.num_noeud= num_noeud and langue = 'en_UK';
SET NEW.libelle_categorie = loc_title;
END IF;
END
DELIMITER ;
Finally , I found the good solution for my case
UPDATE categories c INNER JOIN categories c2 ON (
c.num_noeud = c2.num_noeud
) SET c.libelle_categorie = c2.`libelle_categorie`

Answer 1

Can you clarify?
Are you trying to pull the value from the title column in the 'en_UK' row that exists when you insert an new row with the same id that HAS the title column not entered?
okay
CREATE TRIGGER upd_title BEFORE UPDATE ON `term`
FOR EACH ROW BEGIN
DECLARE loc_title VARCHAR(20);
IF (NEW.title IS NULL OR NEW.title= '') THEN
select title into loc_title from term where NEW.id = id and lang = 'en_UK';
SET NEW.title= loc_title;
END IF;
END
This should do the trick.
This was my trigger def:
CREATE DEFINER = CURRENT_USER TRIGGER `therinks`.`glreturndata_BEFORE_UPDATE` BEFORE UPDATE ON `glreturndata` FOR EACH ROW
BEGIN
DECLARE myVal VARCHAR(20);
if NEW.DESCRIPTION IS NULL or new.description = '' THEN
SELECT min(description) into myVal from glreturndata where category = NEW.category and new.idglreturndata <> idglreturndata;
Set NEW.DESCRIPTION = myval;
end if;
END

Answer 2

It seems that you can't do all this in a trigger. According to the documentation:
Within a stored function or trigger, it is not permitted to modify a table that is already being used (for reading or writing) by the statement that invoked the function or trigger.
According to this answer, it seems that you should:
create a stored procedure, that inserts into/Updates the target table, then updates the other row(s), all in a transaction.
With a stored proc you'll manually commit the changes (insert and update). I haven't done this in MySQL, but this post looks like a good example.