TRIGGER with insert partial field - mysql

Question

2 tables
tb_product :
product_id,
product_size_values
tb_product_category :
product_id ,
category_id
product_size_values contains '41,42,46' or '44,45,46,47' or any values from 42 to 48 with coma separator ....
and the trigger
CREATE TRIGGER trg_product_size AFTER UPDATE ON tb_product
FOR EACH ROW
BEGIN
IF (NEW.product_size_values != OLD.product_size_values) THEN
INSERT INTO tb_product_category (product_id, product_size_values)
VALUES (NEW.product_id, 42) WHERE NEW.product_size_values LIKE '%42%'
;
INSERT INTO tb_product_category (product_id, product_size_values)
VALUES (NEW.product_id, 43) WHERE NEW.product_size_values LIKE '%43%'
;
END IF;
END //
of course the WHERE NEW.product_size_values LIKE does not work
my normal query to do that actually (without trigger ) is
insert into tb_product_category (product_id,category_id)
select product_id,42
from tb_product
where product_size_values like '%42%' ;
insert into tb_product_category (product_id,category_id)
select product_id,43
from tb_product
where product_size_values like '%43%' ;
and NO the comma separated field cannot be changed
thanks for helping

Answer 1

I guess the problem is that you cannot use a like test in a conditional statement and you cannot use a where clause with values and an insert select seems wasteful. You may be able to ditch the like clause and use and instr or locate to check values for example
drop table if exists tb_product,tb_product_category;
create table tb_product
(product_id int,
product_size_values varchar(20));
insert into tb_product values
(1,'42');
create table tb_product_category
(product_id int,
category_id int);
drop trigger if exists trg_product_size;
delimiter $$
CREATE TRIGGER trg_product_size AFTER UPDATE ON tb_product
FOR EACH ROW
BEGIN
IF (NEW.product_size_values != OLD.product_size_values) THEN
if instr(NEW.product_size_values,42) > 0 then
INSERT INTO tb_product_category (product_id, category_id) values (new.product_id,42);
end if;
if INSTR(NEW.product_size_values,43) > 0 then
INSERT INTO tb_product_category (product_id, category_id) values (new.product_id,43);
end if;
END IF;
END $$
delimiter ;
select product_size_values from tb_product;
update tb_product
set product_size_values = '42,43' where product_id = 1;
select * from tb_product_Category;
+------------+-------------+
| product_id | category_id |
+------------+-------------+
| 1 | 42 |
| 1 | 43 |
+------------+-------------+
Works as coded. You may wish to change the insert logic to check for existence before inserting to avoid duplicates.