Question

评分最高的二十部电影（条件：电影应该被至少40位用户评分/观看）？这是我的查询，但它没有给出正确的结果。该数据库包含3个表：

  `select Title 
   from Movie m 
   JOIN
   (select MovieID, Rating 
   from Ratings 
   order by
   Rating)
   as r on 
   m.MovieID = r.MovieID
   limit 20;`

你能建议正确的查询吗？ This image contains the description of tables. It has 3 tables: Movie, Ratings, Users

Answer 1

SQL ORDER BY关键字。 ORDER BY关键字用于按升序或降序对结果集进行排序。 ORDER BY关键字默认按升序对记录进行排序。要按降序对记录进行排序，请使用DESC关键字。欲了解更多信息，请参阅SQL ORDER BY Keyword - W3Schools这样做并获得前20名意味着获得排名前20位的电影。

另一件事是你想要获得前20部电影，所以你可以在进行连接之前从Rating表中获取它们。这将减少连接之前数据集的大小，从而优化查询。

考虑到这些，您的查询应该是：

select Title from Movie m JOIN 
(select MovieID, Rating from Ratings order by Rating DESC limit 20) as r
on m.MovieID = r.MovieID;

Answer 2

IN SQL

select Title from Movie m  
inner join (select top 20 MovieID,sum(Rating) Rate from Ratings group by movieid having count(UserID)>39 order by sum(Rating) DESC) tbl
on m.MovieID=tbl.MovieID
order by tbl.Rate desc

IN MYSQL

 select Title from Movie m  
    inner join (select  MovieID,sum(Rating) Rate from Ratings group by movieid having count(UserID)>39 order by sum(Rating) DESC limit 20) tbl
    on m.MovieID=tbl.MovieID
    order by tbl.Rate desc

电影数据库的SQL查询

2 个答案: