Create trigger for several rows - mysql

Question

I have table users AND orders. After every UPDATE row in orders. I want update DATA in users table namely concat(OLD.DATA + ID which was updated).
Table 'users'.
ID NAME DATA
1 John 1|2
2 Michael 3|4
3 Someone 5
Table 'orders'.
ID USER CONTENT
1 1 ---
2 1 ---
3 2 ---
4 2 ---
5 3 ---
For example:
SELECT `data` from `users` where `id` = 2; // Result: 3|4
UPDATE `orders` SET '...' WHERE `id` > 0;
**NEXT LOOP**
UPDATE `users` SET `data` = concat(OLD.data, ID.rowUpdated) WHERE `user` = 1;
UPDATE `users` SET `data` = concat(OLD.data, ID.rowUpdated) WHERE `user` = 1;
UPDATE `users` SET `data` = concat(OLD.data, ID.rowUpdated) WHERE `user` = 2;
UPDATE `users` SET `data` = concat(OLD.data, ID.rowUpdated) WHERE `user` = 2;
UPDATE `users` SET `data` = concat(OLD.data, ID.rowUpdated) WHERE `user` = 3;
Result:
SELECT data from users where id = 1; // Result: 1|2|1|2
SELECT data from users where id = 2; // Result: 3|4|3|4
SELECT data from users where id = 3; // Result: 5|5
How can I do it?

Answer 1

I think you are making the same mistake I made not too long ago, ie storing an array/object in a column.
I would recommend using the following tables in your scenario:
users
+-----------+-----------+
| id | user_name |
+-----------+-----------+
| 1 | John |
+-----------+-----------+
| 2 | Michael |
+-----------+-----------+
orders
+-----------+-----------+------------+
| id | user_id |date_ordered|
+-----------+-----------+------------+
| 1 | 1 | 2019-03-05 |
+-----------+-----------+------------+
| 2 | 2 | 2019-03-05 |
+-----------+-----------+------------+
Where user_id is the foreign key to users
sales
+-----------+-----------+------------+------------+------------+
| id | order_id | item_sku | qty | price |
+-----------+-----------+------------+------------+------------+
| 1 | 1 | 1001 | 1 | 2.50 |
+-----------+-----------+------------+------------+------------+
| 2 | 1 | 1002 | 2 | 3.00 |
+-----------+-----------+------------+------------+------------+
| 3 | 2 | 1001 | 2 | 2.00 |
+-----------+-----------+------------+------------+------------+
where order_id is the foreign key to orders
Now for the confusing part. You will need to use a series of JOINs to access the relevant data for each user.
SELECT
t3.id AS user_id,
t3.user_name,
t1.id AS order_id,
t1.date_ordered,
SUM((t2.price * t2.qty)) AS order_total
FROM orders t1
JOIN sales t2 ON (t2.order_id = t1.id)
LEFT JOIN users t3 ON (t1.user_id = t3.id)
WHERE user_id=1
GROUP BY order_id;
This will return:
+-----------+--------------+------------+------------+--------------+
| user_id | user_name | order_id |date_ordered| order_total |
+-----------+--------------+------------+------------+--------------+
| 1 | John | 1 | 2019-03-05 | 8.50 |
+-----------+--------------+------------+------------+--------------+
These type of JOIN statements should come up in basically any project using a relational database (that is, if you are designing your DB correctly). Typically I create a view for each of these complicated queries, which can then be accessed with a simple SELECT * FROM orders_view
For example:
CREATE
ALGORITHM = UNDEFINED
DEFINER = `root`#`localhost`
SQL SECURITY DEFINER
VIEW orders_view AS (
SELECT
t3.id AS user_id,
t3.user_name,
t1.id AS order_id,
t1.date_ordered,
SUM((t2.price * t2.qty)) AS order_total
FROM orders t1
JOIN sales t2 ON (t2.order_id = t1.id)
LEFT JOIN users t3 ON (t1.user_id = t3.id)
GROUP BY order_id
)
This can then be accessed by:
SELECT * FROM orders_view WHERE user_id=1;
Which would return the same results as the query above.
Depending on your needs, you will probably need to add a few more tables (addresses, products etc.) and several more rows to each of these tables. Very often you will find that you need to JOIN 5+ tables into a view, and sometimes you might need to JOIN the same table twice.
I hope this helps despite it not exactly answering your question!

Answer 2

It is probably a bad idea to update the USERS table after inserting into (or updating) the ORDERS table. Avoid storing data twice. In your case: you can always get all "order ids" for a user by querying the ORDERS table. Thus, you don't need to store them in the USERS table (again). Example (tested with MySQL 8.0, see dbfiddle):
Tables and data
create table users( id integer primary key, name varchar(30) ) ;
insert into users( id, name ) values
(1, 'John'),(2, 'Michael'),(3, 'Someone') ;
create table orders(
id integer primary key
, userid integer
, content varchar(3) references users (id)
);
insert into orders ( id, userid, content ) values
(101, 1, '---'),(102, 1, '---')
,(103, 2, '---'),(104, 2, '---'),(105, 3, '---') ;
Maybe a VIEW - similar to the one below - will do the trick. (Advantage: you don't need additional columns or tables.)
-- View
-- Inner SELECT: group order ids per user (table ORDERS).
-- Outer SELECT: fetch the user name (table USERS)
create or replace view userorders (
userid, username, userdata
)
as
select
U.id, U.name, O.orders_
from (
select
userid
, group_concat( id order by id separator '|' ) as orders_
from orders
group by userid
) O join users U on O.userid = U.id ;
Once the view is in place, you can just SELECT from it, and you will always get the current "userdata" eg
select * from userorders ;
-- result
userid username userdata
1 John 101|102
2 Michael 103|104
3 Someone 105
-- add some more orders
insert into orders ( id, userid, content ) values
(1000, 1, '***'),(4000, 1, '***'),(7000, 1, '***')
,(2000, 2, ':::'),(5000, 2, ':::'),(8000, 2, ':::')
,(3000, 3, '###'),(6000, 3, '###'),(9000, 3, '###') ;
select * from userorders ;
-- result
userid username userdata
1 John 101|102|1000|4000|7000
2 Michael 103|104|2000|5000|8000
3 Someone 105|3000|6000|9000