棘手的 SQL 查询：加入、分组、拥有

Question

我有以下 tables 用于 SQL 测试；参见 SQLFiddle here

> SELECT * FROM `Movie`;
+-----+-------------------------+------+------------------+
| mID | title                   | year | director         |
+-----+-------------------------+------+------------------+
| 101 | Gone with the Wind      | 1939 | Victor Fleming   |
| 102 | Star Wars               | 1977 | George Lucas     |
| 103 | The Sound of Music      | 1965 | Robert Wise      |
| 104 | E.T.                    | 1982 | Steven Spielberg |
| 105 | Titanic                 | 1997 | James Cameron    |
| 106 | Snow White              | 1937 | <null>           |
| 107 | Avatar                  | 2009 | James Cameron    |
| 108 | Raiders of the Lost Ark | 1981 | Steven Spielberg |
+-----+-------------------------+------+------------------+
> SELECT * FROM Rating;
+-----+-----+-------+------------+
| rID | mID | stars | ratingDate |
+-----+-----+-------+------------+
| 201 | 101 | 2     | 2012-01-22 |
| 201 | 101 | 4     | 2013-01-27 |
| 202 | 106 | 4     | <null>     |
| 203 | 103 | 2     | 2008-01-20 |
| 203 | 108 | 4     | 2002-01-12 |
| 203 | 108 | 2     | 2009-01-30 |
| 204 | 101 | 3     | 2010-01-09 |
| 205 | 103 | 3     | 2010-01-27 |
| 205 | 104 | 2     | 2010-01-22 |
| 205 | 108 | 4     | <null>     |
| 206 | 107 | 3     | 2013-01-15 |
| 206 | 106 | 5     | 2014-01-19 |
| 207 | 107 | 5     | 2000-01-20 |
| 208 | 104 | 3     | 1999-01-02 |
+-----+-----+-------+------------+
> SELECT * FROM Reviewer;
+-----+------------------+
| rID | name             |
+-----+------------------+
| 201 | Sarah Martinez   |
| 202 | Daniel Lewis     |
| 203 | Brittany Harris  |
| 204 | Mike Anderson    |
| 205 | Chris Jackson    |
| 206 | Elizabeth Thomas |
| 207 | James Cameron    |
| 208 | Ashley White     |
+-----+------------------+

我已经解决了所有问题，除了这两个：

1.) 对于每部至少有一个评分的电影，找出电影名称和总星数、最高星和给最高星的人。

我得到了什么：

SELECT m.title, ra.stars, re.name
FROM Movie m
JOIN(
    SELECT R.*
    FROM Rating R
    JOIN(
        SELECT mid, MAX(stars) AS Stars
        FROM Rating
        GROUP BY mid
    ) D ON R.mid = D.mid AND R.Stars = D.Stars
) Ra ON m.mid = ra.mid
JOIN Reviewer re ON ra.rid = re.rid;
+-------------------------+-------+------------------+
| title                   | stars | name             |
+-------------------------+-------+------------------+
| Gone with the Wind      | 4     | Sarah Martinez   |
| Raiders of the Lost Ark | 4     | Brittany Harris  |
| The Sound of Music      | 3     | Chris Jackson    |
| Raiders of the Lost Ark | 4     | Chris Jackson    |
| Snow White              | 5     | Elizabeth Thomas |
| Avatar                  | 5     | James Cameron    |
| E.T.                    | 3     | Ashley White     |
+-------------------------+-------+------------------+

缺少什么：我找不到将每部电影 SUM(stars) 添加到 table 的方法。

2.) 对于同一评论者对同一部电影进行两次评分并在第二次给予更高评分的所有情况，return 评论者的姓名和电影的标题。

到目前为止我得到了什么：

SELECT title, name
FROM Movie m
JOIN Rating ra ON m.mid = ra.mid
JOIN Reviewer re ON ra.rid = re.rid
GROUP BY title, name
HAVING COUNT(*) > 1;
+-------------------------+-----------------+
| title                   | name            |
+-------------------------+-----------------+
| Gone with the Wind      | Sarah Martinez  |
| Raiders of the Lost Ark | Brittany Harris |
+-------------------------+-----------------+

缺少什么：我有所有的电影都被同一个评论者打了两次，但是我不知道如何过滤最新评论比之前评论有更多星星的案例。

如果有人能在这里指出正确的方向，我将不胜感激。 Stack overflow 今天对我帮助很大 :)

编辑：添加我的尝试和遗漏的内容。

Answer 1

这应该给你你想要的第 1 个，第 2 个我需要 sqlfiddle 中的数据来玩弄。同时，我建议查看 lag，尽管 first 和 last 的某种组合可能会满足您的需求。 *请注意，这不会给你准确的答案，它只是一个参考。

select mov.title, sum(rat.stars), max(rat.stars), rev.name
from Movie mov,
  Rating rat,
  Reviewer rev
where mov.mid = rat.mid
and rat.rid = rev.rid
group by mov.title;

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