How to filter the result Mysql - php

Question

Hard to describe what i want, but I will try:
First of all, i have 2 tables: employee and salary. I joined 2 tables by this SQL command:
"SELECT employee.id, employee.employee_name, employee.image, salary.year, salary.month, salary.day, salary.total_salary, salary.id, salary.created
FROM employee
JOIN salary ON salary.employee_id=employee.id"
to get all value i inserted, after execute, i got:
Created name year month day(working) total_salary
------------------------------------------------------------------------------
2016-12-17 20:41 A 2016 1 31 1550000
2016-12-17 21:49 A 2016 1 20 2000000
2016-12-17 22:49 A 2016 2 20 2000000
2016-12-18 22:43 B 2016 2 15 1550000
2016-12-18 23:43 B 2016 2 10 1000000
2016-12-18 23:49 B 2016 2 1 100000
After that, i want to get the newest value per month, so i add this command to the end of sql above:
GROUP BY employee.employee_name, salary.year, salary.month"
and got this:
Created name year month day(working) total_salary
------------------------------------------------------------------------------
2016-12-17 20:41 A 2016 1 31 1550000
2016-12-17 22:49 A 2016 2 20 2000000
2016-12-18 22:43 B 2016 2 15 1550000
What query will return the following result?
Created name year month day(working) total_salary
------------------------------------------------------------------------------
2016-12-17 21:49 A 2016 1 20 2000000
2016-12-17 22:49 A 2016 2 20 2000000
2016-12-18 23:49 B 2016 2 1 100000

Answer 1

My starting point was after your joins, I just made a table that has the data as your first result.
With this query:
SELECT created, name, year, month, day, total_salary FROM
( SELECT * FROM employees
ORDER BY created DESC
) AS sub
GROUP BY name, month, year;
I've got the results you asked for:
Created name year month day(working) total_salary
------------------------------------------------------------------------------
2016-12-17 21:49 A 2016 1 20 2000000
2016-12-17 22:49 A 2016 2 20 2000000
2016-12-18 23:49 B 2016 2 1 100000
Basically the trick was to handle the ordering before you pack them up into groups with GROUP BY
So I made a subQuery that just handles the ordering. This post helped me figure out how to do this.
Here's a Fiddle where you can play around and adjust it to your starting query.

Answer 2

Before you group you should sort the entries by created date the newest entries are first:
ORDER BY salary.created DESC
Change the first query (you have to remove or alias one of the id's because you will have two columns with the same name):
SELECT employee.id as employee_id, employee.employee_name, employee.image, salary.year, salary.month, salary.day, salary.total_salary, salary.id, salary.created
FROM employee JOIN salary ON salary.employee_id=employee.id
ORDER BY salary.created DESC
So the last created are shown first. Then group the results like you did:
SELECT * FROM (
SELECT employee.id as employee_id, employee.employee_name, employee.image, salary.year, salary.month, salary.day, salary.total_salary, salary.id, salary.created
FROM employee
JOIN salary ON salary.employee_id=employee.id
ORDER BY salary.created DESC
) as employee_salary
GROUP BY employee_salary.employee_name, employee_salary.year, employee_salary.month