Inner Join table with a maximum date - mysql

Question

Please help me.
I have 2 table Users and Diseaselogs
1 user has many diseaselogs
I want to select all users and each user must be field date in diseaselogs is max
Data example
Users
id | name | age
1 | Nam | 21
2 | Thao | 23
3 | An | 19
Diseaselogs
id | logType | userId | date
1 | positive | 1 | 2021-06-21
2 | negative | 2 | 2021-06-22
3 | pending | 1 | 2021-06-24
4 | negative | 1 | 2021-06-26
5 | negative | 2 | 2021-06-21
6 | pending | 3 | 2021-06-23
7 | negative | 1 | 2021-06-24
8 | negative | 2 | 2021-06-25
9 | pending | 3 | 2021-06-28
Expect output
id | name | logId | logType | date
1 | Nam | 4 | negative | 2021-06-26
2 | Thao | 8 | negative | 2021-06-25
3 | An | 9 | pending | 2021-06-28

Answer 1

As ROW_NUMBER() doesn't support lower version of mysql i.e 5.7 to downwords. So I've tried here alternatives of ROW_NUMBER().
-- MySQL (V 5.6)
SELECT u.id, u.name, tmp.logId, tmp.logType, tmp.date
FROM users u
INNER JOIN (SELECT #row_no := IF(#prev_val = t.userId, #row_no + 1, 1) AS row_number
, #prev_val := t.userId AS userId
, t.date
, t.logType
, t.id AS logId
FROM Diseaselogs t,
(SELECT #row_no := 0) x,
(SELECT #prev_val := '') y
ORDER BY t.userId, t.date DESC ) tmp
ON u.id = tmp.userId
AND tmp.row_number = 1;
Please check url http://sqlfiddle.com/#!9/741b96/16
Also if your MySQL version is 5.8 then you can apply the below query where row_number() is used.
SELECT u.id, u.name, tmp.logId, tmp.logType, tmp.date
FROM users u
INNER JOIN (SELECT ROW_NUMBER() OVER (PARTITION BY userId ORDER BY date DESC) row_number
, userId
, date
, logType
, id AS logId
FROM Diseaselogs ) tmp
ON u.id = tmp.userId
AND tmp.row_number = 1;

Answer 2

in mysql 8 you can use ROW_NUMBER and an INNER JOIN
in prior versions you need to use another method for rownumber
Schema (MySQL v8.0)
CREATE TABLE Diseaselogs (
`id` INTEGER,
`logType` VARCHAR(8),
`userId` INTEGER,
`date` VARCHAR(10)
);
INSERT INTO Diseaselogs
(`id`, `logType`, `userId`, `date`)
VALUES
('1', 'positive', '1', '2021-06-21'),
('2', 'negative', '2', '2021-06-22'),
('3', 'pending', '1', '2021-06-24'),
('4', 'negative', '1', '2021-06-26'),
('5', 'negative', '2', '2021-06-21'),
('6', 'pending', '3', '2021-06-23'),
('7', 'negative', '1', '2021-06-24'),
('8', 'negative', '2', '2021-06-25'),
('9', 'pending', '3', '2021-06-28');
CREATE TABLE users (
`id` INTEGER,
`name` VARCHAR(4),
`age` INTEGER
);
INSERT INTO users
(`id`, `name`, `age`)
VALUES
('1', 'Nam', '21'),
('2', 'Thao', '23'),
('3', 'An', '19');
Query #1
SELECT
u.id, `name`, t1.id,`logType`, `date`
FROM
(SELECT
id,`logType`, `userId`, `date`
, ROW_NUMBER() OVER (PARTITION BY `userId` ORDER BY `date` DESC) rn
FROM
Diseaselogs) t1
INNER JOIN users u ON t1.userId = u.id
WHERE rn = 1;
id
name
id
logType
date
1
Nam
4
negative
2021-06-26
2
Thao
8
negative
2021-06-25
3
An
9
pending
2021-06-28
View on DB Fiddle
Schema (MySQL v8.0)
CREATE TABLE Diseaselogs (
`id` INTEGER,
`logType` VARCHAR(8),
`userId` INTEGER,
`date` VARCHAR(10)
);
INSERT INTO Diseaselogs
(`id`, `logType`, `userId`, `date`)
VALUES
('1', 'positive', '1', '2021-06-21'),
('2', 'negative', '2', '2021-06-22'),
('3', 'pending', '1', '2021-06-24'),
('4', 'negative', '1', '2021-06-26'),
('5', 'negative', '2', '2021-06-21'),
('6', 'pending', '3', '2021-06-23'),
('7', 'negative', '1', '2021-06-24'),
('8', 'negative', '2', '2021-06-25'),
('9', 'pending', '3', '2021-06-28');
CREATE TABLE users (
`id` INTEGER,
`name` VARCHAR(4),
`age` INTEGER
);
INSERT INTO users
(`id`, `name`, `age`)
VALUES
('1', 'Nam', '21'),
('2', 'Thao', '23'),
('3', 'An', '19');
Query #1
SELECT
u.id, `name`, `age`,`logType`, `date`
FROM
(SELECT
`logType`, `userId`, `date`
, ROW_NUMBER() OVER (PARTITION BY `userId` ORDER BY `date` DESC) rn
FROM
Diseaselogs) t1
INNER JOIN users u ON t1.userId = u.id
WHERE rn = 1;
id
name
age
logType
date
1
Nam
21
negative
2021-06-26
2
Thao
23
negative
2021-06-25
3
An
19
pending
2021-06-28
View on DB Fiddle