how to minimize the response time for this query in mysql - php

Question

I have table having list of football matches. it has columns like match_id, team a score, team 2 score, rounds, match_date etc.
I need all rows from database with highest margin of that round
margin is difference of team a score and team b score.
my query is
SELECT *,( SELECT MAX(ABS((z.home_score - z.away_score)))
FROM tblform_matches z
WHERE YEAR(z.match_date) = YEAR(tblform_matches.match_date)
AND z.round = tblform_matches.round ) as highest_margin
from tblform_matches where some condtion
it is a simplified query where some condition is a large query string to select some specified matches according to filter.
currently there are around 5000 matches in database.
Due to sub-query my page is taking 4 more seconds to load.
there are 9 matches in each round and there are more than 20 rounds in every year
I am executing the above query for every team in php loop. I cant change this thing. as there are a lot of calculation for showing stats.
Sorry if my question is uncleared, I am here if I missed something as I am a new bee to stakoverflow
Thanks in advance.

Answer 1

This is your query:
SELECT m.*,
(SELECT MAX(ABS((m2.home_score - m2.away_score)))
FROM tblform_matches m2
WHERE YEAR(m2.match_date) = YEAR(m.match_date) AND
m2.round = m.round
) as highest_margin
from tblform_matches m
where some condition;
Presumably, the best way to optimize this is to focus on . Oh well. You will want the right indexes there.
Indexes are clearly the solution, but you have a problem because the of the year function. And easy solution is to use indequalities:
SELECT m.*,
(SELECT MAX(ABS((m2.home_score - m2.away_score)))
FROM tblform_matches m2
WHERE m2.round = m.round
(m2.match_date >= makedate(year(m.match_date), 1) and
m2.match_date < makedate(year(m.match_date) + 1, 1)
)
) as highest_margin
from tblform_matches m
where some condtion;
The best index for the subquery is tblform_matches(round, match_date, home_score, away_score). The first two columns are used for the where clause. The second two for the select.
Note: if you made two relatively minor changes to the data structure, this could work even better. Add a column for the year of the match date (redundant, but important for indexing). And, add a column for the absolute value of the difference between the scores. Then the query would be:
SELECT m.*,
(SELECT MAX(score_diff)
FROM tblform_matches m2
WHERE m2.round = m.round and m2.matchyear = m.matchyear
) as highest_margin
from tblform_matches m
where some condtion;
The index on this query would be: tblform_matches(round, matchyear, score_diff) and the lookup should be pretty fast.
EDIT:
You may get better performance with an explicit join:
SELECT m.*, m2.highest_margin
from tblform_matches m join
(select MAX(ABS((m2.home_score - m2.away_score))) as highest_margin
from tblform_matches m2
group by year(m2.match_date), m2.round
) m2
on year(m.match_date) = year(m2.match_date) and m2.round = m.round
where some condition;