mysql count votes optimization - mysql

Question

so im making a file hub nothing huge or fancy just to store some files that may be shared by others for download. and it just occured to me in the way that i originally intended to count the amount of upvotes or downvotes the query could be server heavy.the query to get the files is something along the lines of
select*from files;
and in such i would recieve an array of my files that i could loop over and get specifics on each file now with the inclusion of voting a file that same foreach loop would include a further query that would get the count the amount votes a file would get (the file id in the where clause) like so
select*from votes where upvoted=true and file.id=?
and i was thinking of using pdo::rowCount to get my answer. now evey bone in my body just says this is bad very bad as imagine im getting 10,000 files i just ran 10,000 extra queries one on each file and i havent looked at the downvotes yet which i was think could go in a similar fasion. any optimization adviece here is a small rep of the structure of a few tables. the upvoted and downvoted columbs are of type bool or tinyint if you will
table: file table: user table: votes
+----+-------------+ +----+-------------+ +--------+--------+--------+--------+
| id |storedname | | id | username | |file_id | user_id| upvoted | downvoted
+----+-------------+ +----+-------------+ +--------+--------+--------+--------+
| 1 | 45tfvb.txt | | 1 | matthew | | 1 | 2 | 1 | 0
| 2 |jj7fnfddf.pdf| | 2 | mark | | 2 | 1 | 1 | 1
| .. | .. | | .. | .. | | .. | .. | .. | ..

Answer 1

there are two ways to do this. the better way to do this (aka faster) is to write separate queries and build into one variable in your programming language (like php, python.. etc.)
SELECT
d.id as doc_id,
COUNT(v.document_id) as num_upvotes
FROM votes v
JOIN document d on d.id = v.document_id
WHERE v.upvoted IS TRUE
GROUP BY doc_id
);
that will return your list of upvoted documents. you can do the same for your downvotes.
then after your select from document do a for loop to compare the votes with the document by ID and build into a dictionary or list.
The second way to do this which can take a lot longer at runtime if you have a bunch of records in the table (its less efficient, but easier to write) is to add subquery selects in your select statement like this...
SELECT
logical_name ,
document.id ,
file_type ,
physical_name ,
uploader_notes ,
views ,
downloads ,
user.name ,
category.name AS category_name,
(Select count(1) from votes where upvoted=true and document_id=document.id )as upvoted,
(select count(1) from votes where upvoted=false and document_id=document.id) as downvoted
FROM document
INNER JOIN category ON document.category_id = category.id
INNER JOIN user ON document.uploader_id = user.id
ORDER BY category.id

Answer 2

Two advices:
Avoid SELECT * especially if you're going to count. Replace it, with something like that:
SELECT COUNT(1) AS total WHERE upvoted=true AND file.id=?
Maybe you want to create a TRIGGER to keep update a counter in the file table.
I hope it will be helpfull to you.