Create a table in a trigger and compare it - mysql

Question

i have 4 tables and i want to create a trigger that it declares a table and store it all in that table so it can be compared latter.
CREATE TABLE IF NOT EXISTS `inventory` (
`id_product` INT(4) ZEROFILL NOT NULL AUTO_INCREMENT,
`model` varchar(45) NOT NULL,
`price_new` FLOAT DEFAULT '0',
`launch_date` DATE NOT NULL,
`stock` INT DEFAULT '0',
PRIMARY KEY (`id_product`));
CREATE TABLE IF NOT EXISTS `order` (
`id_order` INT(4) ZEROFILL NOT NULL AUTO_INCREMENT,
`id_customer` INT(6) ZEROFILL NOT NULL,
`subtotal` FLOAT DEFAULT '0',
`discount` float DEFAULT '0',
`tax_rate` float DEFAULT '0.23',
`total` float DEFAULT '0',
`date` DATETIME DEFAULT NOW(),
PRIMARY KEY (`id_order`),
CONSTRAINT `fk_order_1`
FOREIGN KEY (`id_customer`)
REFERENCES `iSAVE`.`customer` (`id_customer`)
ON DELETE RESTRICT
ON UPDATE CASCADE);
CREATE TABLE IF NOT EXISTS `order_item` (
`id_order_item` INT(4) ZEROFILL NOT NULL AUTO_INCREMENT PRIMARY KEY,
`id_product` INT(4) ZEROFILL NOT NULL,
`id_order` INT(4) ZEROFILL NOT NULL,
`quantity` INT DEFAULT NULL,
FOREIGN KEY (`id_product`) REFERENCES `iSAVE`.`inventory` (`id_product`),
FOREIGN KEY (`id_order`) REFERENCES `iSAVE`.`order` (`id_order`)
);
CREATE TABLE IF NOT EXISTS `transaction` (
`id_transaction` INT(4) ZEROFILL NOT NULL AUTO_INCREMENT PRIMARY KEY,
`id_order` INT(4) ZEROFILL NOT NULL,
`status` char(20) default 'Not completed',
FOREIGN KEY (`id_order`) REFERENCES `iSAVE`.`order` (`id_order`)
);
In here are the tables that im using. But now i have a trigger that after insert on orders it inserts on transactions. My objective now its to create a trigger that generates a table that takes order and order item and store id_product id_order and quantity so it can be used to after update on transaction the stock is changed on the respective items on tabel inventory.
This is the trigger that i have so far but i cant use it because i dont rly know how to declare a table in mysql:
delimiter $$
CREATE TRIGGER trigg1 after update on `transaction` for each row
BEGIN
declare #item TABLE(
id_order int,
id_product int,
quantity int);
update inventory i join #item it using (id_product)
set i.stock = i.stock - it.quantity
where it.id_order = new.id_order;
end $$
delimiter ;

Answer 1

You can't you have to use a temporaRY TABLE
delimiter $$
CREATE TRIGGER trigg1 after update on `transaction` for each row
BEGIN
CREATE TEMPORARY TABLE tbl1(
id_order int,
id_product int,
quantity int);
update inventory i join tbl1 it using (id_product)
set i.stock = i.stock - it.quantity
where it.id_order = new.id_order;
DROP TEMPORARY TABLE tbl1;
end $$
delimiter ;
But usually you make a temporaray atble with a select
CREATE TEMPORARY TABLE tbl1
SELECT id_order ,
id_product ,
quantity
FROM ORDERS