MySQL table order by values from relation table by newest date - mysql

Question

Is it possible to select from mySQL table rows ordered by joined table values by current date?
Maybe I show it. I Have two tables:
One country have many scores GROUPED BY date. Is it possible to sort countries by current date scores?
I have countires with scores from table in PHP arrays:
$countries = array(
'England' =>
array('name', 'tag',
'scores' => array(
0 => array('date' => '2018-07', 'score' => 100),
1 => array('date' => '2018-08', 'score' => 50)
)),
'USA' =>
array('name', 'tag',
'scores' => array(
0 => array('date' => '2018-08', 'score' => 50),
1 => array('date' => '2018-09', 'score' => 20)
)
),
'France' =>
array('name', 'tag',
'scores' => array(
0 => array('date' => '2018-08', 'score' => 30),
1 => array('date' => '2018-09', 'score' => 100)
)
)
);
I need to select countries ordered by scores for current date. Lets say current date is 2018-09. I need to search countries and sort them like this:
$countries = array(
'France' =>
array('name', 'tag',
'scores' => array(
0 => array('date' => '2018-08', 'score' => 30),
1 => array('date' => '2018-09', 'score' => 100)
)
),
'USA' =>
array('name', 'tag',
'scores' => array(
0 => array('date' => '2018-08', 'score' => 50),
1 => array('date' => '2018-09', 'score' => 20)
)
),
'England' =>
array('name', 'tag',
'scores' => array(
0 => array('date' => '2018-07', 'score' => 100),
1 => array('date' => '2018-08', 'score' => 50)
)),
);
England is last becouse havent scores for date '2018-09'
Second is France becouse for date '2018-09' have 100 points
USA is last becosue for date '2018-09' have 20 points
SELECT c.name, s.date, s.score FROM country c LEFT JOIN score s ON s.country_id=c.id GROUP BY date ORDER BY (??)

Answer 1

We could do something like this, to get the latest score date for each country_id, along with the score for that latest date, and then order by those values:
SELECT c.name
, s.date
, s.score
FROM country c
LEFT
JOIN score s
ON s.country_id = c.id
LEFT
JOIN ( SELECT m.country_id
, MAX(m.date) AS max_date
FROM score m
GROUP
BY m.country_id
) n
ON n.country_id = c.id
LEFT
JOIN score o
ON o.country_id = n.country_id
AND o.date = n.max_date
ORDER
BY o.date DESC
, o.score DESC
, c.name ASC
, s.date ASC
Note that this assumes that the (country_id,date) tuple is unique in the score table. If we don't have that guarantee, we can tweak the query to accommodate that. Something like this:
SELECT c.name
, s.date
, s.score
FROM country c
LEFT
JOIN score s
ON s.country_id = c.id
LEFT
JOIN ( SELECT o.country_id
, o.date
, MAX(o.score) AS max_date_score
FROM ( SELECT m.country_id
, MAX(m.date) AS max_date
FROM score m
GROUP
BY m.country_id
) n
JOIN score o
ON o.country_id = n.country_id
AND o.date = n.max_date
GROUP
BY o.country_id
, o.date
) p
ON p.country_id = c.id
ORDER
BY p.date DESC
, p.max_date_score DESC
, c.name ASC
, s.date ASC
, s.score DESC