Getting most recent row per group in MySQL [duplicate] - mysql

Question

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Retrieving the last record in each group - MySQL
(33 answers)
Closed 3 years ago.
I am trying to get all most recent Paper.material's for each Book.isbn. I am using left to get the base of each Book.isbn, since they can have a suffix that indicates the revision, for example : 'X1726748384Z1' or 'X1837943875Z2' etc.. I tried over partition by but it didn't work because MySQL 5.7 doesn't support this. How can I make this work?
GOAL
For each Book.isbn as X:
select left(Book.isbn, 11) BaseISBN, Paper.material, Book.date
from Book
join Page on Book.id = Page.book_id
join Paper on Page.id = Paper.page_id
where Book.name = 'world'
and left(Book.isbn, 11) = X <--
and Page.name = 'test'
order by Book.date desc
limit 1
QUERY
select left(Book.isbn, 11) BaseISBN, Paper.material, max(Book.date)
from Book
join Page on Book.id = Page.book_id
join Paper on Page.id = Paper.page_id
where Book.name = 'world'
and left(Book.isbn, 11) in('X1726748384', 'X1837943875')
and Page.name = 'test'
group by left(Book.isbn, 11);
RETURNS
| Book.isbn | Paper.material | max(Book.date) |
|-------------|----------------|----------------------|
| X1726748384 | 10134248300B | 2018-01-01T00:00:00Z |
| X1837943875 | 10985782343F | 2021-01-01T00:00:00Z |
etc...
SHOULD RETURN
| Book.isbn | Paper.material | max(Book.date) |
|-------------|----------------|----------------------|
| X1726748384 | 10985782343E | 2018-01-01T00:00:00Z |
| X1837943875 | 10985782343H | 2021-01-01T00:00:00Z |
etc...
SQL FIDDLE
And DDLs of same:
CREATE TABLE `Book` (
`id` INT NOT NULL AUTO_INCREMENT,
`isbn` varchar(255),
`name` varchar(255),
`date` DATETIME,
PRIMARY KEY (`id`)
);
CREATE TABLE `Page` (
`id` INT NOT NULL AUTO_INCREMENT,
`name` varchar(255),
`book_id` INT NOT NULL,
PRIMARY KEY (`id`)
);
CREATE TABLE `Paper` (
`id` INT NOT NULL AUTO_INCREMENT,
`material` varchar(255),
`page_id` INT NOT NULL,
PRIMARY KEY (`id`)
);
ALTER TABLE `Page` ADD CONSTRAINT `Page_fk0` FOREIGN KEY (`book_id`) REFERENCES `Book`(`id`);
ALTER TABLE `Paper` ADD CONSTRAINT `Paper_fk0` FOREIGN KEY (`page_id`) REFERENCES `Page`(`id`);
INSERT INTO `Book` (`isbn`, `name`, `date`) VALUES
('X1234234403', 'hello', '2016-01-01'),
('X1726748384', 'world', '2017-01-01'),
('X1726748384Z1', 'world', '2018-01-01'),
('X1837943875', 'world', '2019-01-01'),
('X1837943875Z1', 'world', '2020-01-01'),
('X1837943875Z2', 'world', '2021-01-01');
INSERT INTO `Page` (`name`, `book_id`) VALUES
('bla', 1),
('test', 2),
('test', 3),
('test', 4),
('test', 5),
('test', 6);
INSERT INTO `Paper` (`material`, `page_id`) VALUES
('10134248300A', 1),
('10134248300B', 2),
('10134248300C', 2),
('10985782343D', 3),
('10985782343E', 3),
('10985782343F', 4),
('10985782343G', 5),
('10985782343H', 6);

Answer 1

'Etc.' is not very useful when trying to understand what should and shouldn't be included in a result.
Nevertheless, perhaps you're after something a bit like this...
SELECT b.*
, z.material
FROM book b
JOIN
( SELECT LEFT(isbn,11) isbn11
, MAX(date) date
FROM book
WHERE
( isbn LIKE 'X1726748384%'
OR isbn LIKE 'X1837943875%'
)
AND name = 'world'
GROUP
BY isbn11
) x
ON x.isbn11 = LEFT(b.isbn,11)
AND x.date = b.date
JOIN page y
ON y.book_id = b.id
JOIN paper z
ON z.page_id = y.id
WHERE y.name = 'test';
+----+---------------+-------+---------------------+--------------+
| id | isbn | name | date | material |
+----+---------------+-------+---------------------+--------------+
| 3 | X1726748384Z1 | world | 2018-01-01 00:00:00 | 10985782343D |
| 3 | X1726748384Z1 | world | 2018-01-01 00:00:00 | 10985782343E |
| 6 | X1837943875Z2 | world | 2021-01-01 00:00:00 | 10985782343H |
+----+---------------+-------+---------------------+--------------+
3 rows in set (0.00 sec)