如何計算MySQL中的投票？

Question

我有一個名爲votes的數據庫表，其中包含三列「時間戳」，「選民」和「voteed_for」。

表中的每個條目代表一票。我想在某些條件下爲每個「投票」選出所有選票。

的條件如下：

• 每個選民可以通過一個單一的選民最近的投票數只能投票一次，在多票的情況。

• 只有在指定時間之前進行的選票纔會被統計。

Answer 1

試試這個：

SELECT voted_for, count(*) 
FROM votes v 
INNER JOIN (SELECT Voter, Max(timestamp) as lastTime from votes group by Voter) A 
on A.Voter = v.voter and a.lasttime = v.timestamp 
WHERE timestamp < {date and time of last vote allowed} 
Group by voted_for 

Answer 2

SELECT voted_for,COUNT(DISTINCT voter) 
FROM votes 
WHERE timestamp < '2010-11-18 21:05:00' 
GROUP BY voted_for 

Answer 3

下面可能證明是有益的：

drop table if exists users; 
create table users 
( 
user_id int unsigned not null auto_increment primary key, 
username varbinary(32) not null, 
unique key users_username_idx(username) 
)engine=innodb; 

insert into users (username) values 
('f00'),('foo'),('bar'),('bAr'),('bish'),('bash'),('bosh'); 

drop table if exists picture; 
create table picture 
( 
picture_id int unsigned not null auto_increment primary key, 
user_id int unsigned not null, -- owner of the picture, the user who uploaded it 
tot_votes int unsigned not null default 0, -- total number of votes 
tot_rating int unsigned not null default 0, -- accumulative ratings 
avg_rating decimal(5,2) not null default 0, -- tot_rating/tot_votes 
key picture_user_idx(user_id) 
)engine=innodb; 

insert into picture (user_id) values 
(1),(2),(3),(4),(5),(6),(7),(1),(1),(2),(3),(6),(7),(7),(5); 


drop table if exists picture_vote; 
create table picture_vote 
( 
picture_id int unsigned not null, 
user_id int unsigned not null,-- voter 
rating tinyint unsigned not null default 0, -- rating 0 to 5 
primary key (picture_id, user_id) 
)engine=innodb; 

delimiter # 

create trigger picture_vote_before_ins_trig before insert on picture_vote 
for each row 
proc_main:begin 

declare total_rating int unsigned default 0; 
declare total_votes int unsigned default 0; 

if exists (select 1 from picture_vote where 
    picture_id = new.picture_id and user_id = new.user_id) then 
     leave proc_main; 
end if; 

select tot_rating + new.rating, tot_votes + 1 into total_rating, total_votes 
    from picture where picture_id = new.picture_id; 

-- counts/stats 
update picture set 
    tot_votes = total_votes, 
    tot_rating = total_rating, 
    avg_rating = total_rating/total_votes 
where picture_id = new.picture_id; 

end proc_main # 

delimiter ; 

insert into picture_vote (picture_id, user_id, rating) values 
(1,1,5),(1,2,3),(1,3,3),(1,4,2),(1,5,1), 
(2,1,1),(2,2,2),(2,3,3),(2,4,4),(2,5,5),(2,6,1),(2,7,2), 
(3,1,5),(3,2,5),(3,3,5),(3,4,5),(3,5,5),(3,6,5),(3,7,5); 

select * from users order by user_id; 
select * from picture order by picture_id; 
select * from picture_vote order by picture_id, user_id;