嗨,我正在创建一个数据库,用于跟踪用户对我们的产品投票的次数。
是否有一种方法,我可以改变下面的查询,以计算每年的最大票数?我正在使用Oracle SQL developer
创建表的结构为
Members(username, email, pwd)
Votes (username*, prodCode*, score, voteDate)
注意:
SELECT username, count(username)
FROM Votes NATURAL JOIN members
GROUP BY username, email
HAVING COUNT(*) >= All(SELECT count(username)
FROM Votes v1
GROUP BY username);
我不完全确定我理解你的问题,但这样的东西也许?
SELECT username,
extract(year from voteDate) as vote_year,
count(*) as votes_per_year,
max(count(*)) over (partition by extract(year from voteDate)) as max_votes_per_year
FROM Votes vt
GROUP BY username, extract(year from voteDate);
这将为您提供每个用户和年份的计数以及每行中每年的最大计数。(注意,这里不需要成员表,因为显然不需要其中的任何列)。
如果您需要显示没有人投票的年份(或某个特定用户没有投票)的零计数,那么您需要这样的内容:
with years as (
select 2009 + level as year
from dual
connect by level <= 21
)
SELECT username,
y.year,
count(vt.username) as votes_per_year,
max(count(vt.username)) over (partition by y.year) as max_votes_per_year
FROM years y
LEFT JOIN Votes vt on y.year = extract(year from vt.voteDate)
GROUP BY username, y.year
order by y.year, username;
这将使用公共表表达式(with ...
)"实时"生成2010年到2030年之间的年份列表。您可以调整CTE以延长或缩小年数。
为此,您最好有一个年份表(或者至少有一个数字表,可以帮助您设置一组年份)。
SELECT
username
, MAX(cnt) AS mcnt
FROM (
SELECT
username
, count(username) AS cnt
FROM members
CROSS JOIN Years
INNER JOIN Votes ON (
members.username = Votes.username -- using an INT here would be more efficient
AND
Votes.voteDate >= Years.firstJanuary
AND
Votes.voteDate < Years.firstJanuary+ 1 Year -- Pseudo code, you didn't mention any DBMS
)
GROUP BY username, prodCode, Years.firstJanuary
) AS X