SQL/MySQL - Update target table with most recent entry - mysql

Question

I'm looking for some help with a SQL/MySQL problem.
I have three source tables:
CREATE TABLE `customers` (
`cid` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`customer_name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8
CREATE TABLE `standards` (
`sid` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`standard_name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`sid`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8
CREATE TABLE `partial_standard_compliance` (
`customer` bigint(20) unsigned NOT NULL,
`standard` bigint(20) unsigned NOT NULL,
`standard_compliance` bigint(20) unsigned DEFAULT NULL,
`created_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8
The idea is a customer gives themselves a rating using the standard_compliance column in the partial_standard_compliance table.
Customers can rate the same standard multiple times.
Result example:
+----------+----------+---------------------+---------------------+
| customer | standard | standard_compliance | created_time |
+----------+----------+---------------------+---------------------+
| 1 | 1 | 50 | 2023-01-28 16:19:34 |
| 1 | 1 | 60 | 2023-01-28 16:19:40 |
| 1 | 1 | 70 | 2023-01-28 16:19:48 |
| 2 | 10 | 30 | 2023-01-28 16:58:21 |
| 2 | 8 | 60 | 2023-01-28 16:58:32 |
| 2 | 9 | 60 | 2023-01-28 16:58:39 |
| 2 | 9 | 80 | 2023-01-28 16:58:43 |
+----------+----------+---------------------+---------------------+
I need to create a 4th table that has customer name, standard name and the most recent rating they have given themselves.
I have been trying with JOINS and CREATE AS SELECT, but haven't been able to solve it.
Any point in the right direction would be great. Thanks.
I have been trying with JOINS and CREATE AS SELECT

Answer 1

I need to create a 4th table that has customer name, standard name and
the most recent rating they have given themselves
Would be better if you create a view instead.
create view fourth_table as
select customer_name ,
standard_name ,
standard_compliance,
created_time
from (select c.customer_name,
s.standard_name,
psc.standard_compliance,
psc.created_time,
row_number() over(partition by c.customer_name order by psc.created_time desc ) as rn
from customers c
inner join partial_standard_compliance psc on psc.customer=c.cid
inner join standards s on s.sid=psc.standard
) x
where rn=1;
https://dbfiddle.uk/ZiK-k8jN
MySQL View