[英]How to write sql query using group by
我有這張桌子:
actors(id: int, first_name: string, last_name: string, gender: string)
directors(id: int, first_name: string, last_name: string)
directors genres(director id: int, genre: string, prob:
float)
movies(id: int, name: string, years: int, rank:
float,)
movies directors(director id: int, movie id: int)
movies genres(movie id: int, genre: string)
roles(actor id: int, movie id: int, role: string)
我想查找每種類型的年份,在該年份中制作該類型的電影最多。
我正在執行以下操作,但遇到問題,請幫忙!
select m.YEAR, count(m.year) as c, genre
from movies_genres,
movies m
where m.id = movies_genres.movie_id
group by genre, m.year;
您將獲得每年每種流派的電影數量,這非常好。 現在,您只需要通過將查詢作為派生表來選擇最大值。
select genre, year, max(c) mc
from
(select m.YEAR, count(m.year) as c, genre
from movies_genres mg
inner join movies m
on m.id = mg.movie_id
group by genre, m.year)
group by genre, year
如果您使用的是SQL Server或Oracle或DB2,則應該可以使用。
SELECT genre, year, number
FROM
(
SELECT genre, year, number,
row_number() over (PARTITION BY genre ORDER BY number DESC) as rank
FROM
(
SELECT mg.genre, m.year, count(*) as number
FROM movies_genres mg
JOIN movies m on m.id = mg.movie_id
GROUP BY mg.genre, m.year
) A
) B
WHERE rank = 1
工作原理:從內到外,首先您要獲得所有流派和年份的計數。 然后,您可以按計數對每種類型的年份進行排名,最后選擇最大的項。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.