Question

我正在制作一个应用程序，可以显示人们对电影的评分，不论是热门还是热门。我想写一个查询来获取电影评分的次数。评级表如下所示：

| id | winner | loser |
| 1  |   1    |   2   |
| 2  |   2    |   3   |
| 3  |   1    |   3   |

通过运行这样的查询，我可以获得电影“赢了”的次数：

SELECT winner, count(winner) AS number_of_wins
  FROM movie_results
  GROUP BY winner
  ORDER BY number_of_wins DESC;

但是我希望得到另一个查询，显示电影与其他电影相关的总次数，即电影似乎被评级的次数，是否被评为高于或低于另一部电影。仅使用SQL查询实现此目的的最简单方法是什么？

Answer 1

以下是一种方法，使用becomes：

union all

Answer 2

您可以在两个派生表之间执行full join，其中每个表包含每个玩家的损失和获胜次数。

select 
    coalesce(winner,loser) player,
    coalesce(number_of_wins,0) number_of_wins,
    coalesce(number_of_losses,0) number_of_losses,
    coalesce(number_of_wins,0) + coalesce(number_of_losses,0) number_of_matches 
from (
    select winner, count(*) number_of_wins
    from movie_results
    group by winner
) winners full join (
    select loser, count(*) number_of_losses
    from movie_results
    group by loser
) losers on losers.loser = winners.winner

http://sqlfiddle.com/#!15/980d6/3

计算多个列中的出现次数

2 个答案: