联合 - 关键字“order”附近的语法不正确

Question

Table: Movies

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| movie_id      | int     |
| title         | varchar |
+---------------+---------+

movie_id is the primary key for this table. title is the name of the movie. Table: Users

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| user_id       | int     |
| name          | varchar |
+---------------+---------+

user_id is the primary key for this table. Table: Movie_Rating

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| movie_id      | int     |
| user_id       | int     |
| rating        | int     |
| created_at    | date    |
+---------------+---------+

(movie_id, user_id) is the primary key for this table. This table contains the rating of a movie by a user in their review. created_at is the user's review date.

Write the following SQL query:

Find the name of the user who has rated the greatest number of the movies. In case of a tie, return lexicographically smaller user name.

Find the movie name with the highest average rating in February 2020. In case of a tie, return lexicographically smaller movie name.

Query is returned in 2 rows, the query result format is in the folowing example:

Movies table:

+-------------+--------------+
| movie_id    |  title       |
+-------------+--------------+
| 1           | Avengers     |
| 2           | Frozen 2     |
| 3           | Joker        |
+-------------+--------------+

Users table:

+-------------+--------------+
| user_id     |  name        |
+-------------+--------------+
| 1           | Daniel       |
| 2           | Monica       |
| 3           | Maria        |
| 4           | James        |
+-------------+--------------+

Movie_Rating table:

+-------------+--------------+--------------+-------------+
| movie_id    | user_id      | rating       | created_at  |
+-------------+--------------+--------------+-------------+
| 1           | 1            | 3            | 2020-01-12  |
| 1           | 2            | 4            | 2020-02-11  |
| 1           | 3            | 2            | 2020-02-12  |
| 1           | 4            | 1            | 2020-01-01  |
| 2           | 1            | 5            | 2020-02-17  | 
| 2           | 2            | 2            | 2020-02-01  | 
| 2           | 3            | 2            | 2020-03-01  |
| 3           | 1            | 3            | 2020-02-22  | 
| 3           | 2            | 4            | 2020-02-25  | 
+-------------+--------------+--------------+-------------+

Result table:

+--------------+
| results      |
+--------------+
| Daniel       |
| Frozen 2     |
+--------------+

Daniel and Maria have rated 3 movies ("Avengers", "Frozen 2" and "Joker") but Daniel is smaller lexicographically. Frozen 2 and Joker have a rating average of 3.5 in February but Frozen 2 is smaller lexicographically.

Here is my solution:

(
  select top 1 u.name as results 
  from users as u
  join movie_rating as m on u.user_id = m.user_id
  group by user_id
  order by count(rating) desc, name
)
union all
(
  select top 1 m.title as results 
  from movies as m
  join movie_rating as r on m.movie_id = r.movie_id
  where CONVERT(varchar(7), r.created_at, 121) = '2020-02'
  group by m.title
  order by avg(rating) desc, m.title
);

I get this error that I can't figure it out

[42000] [Microsoft][ODBC Driver 13 for SQL Server][SQL Server]Incorrect syntax near the keyword 'order'. (156) (SQLExecDirectW)

any idea and how to fix it?

Answer 1

OK I think this might work, as you didn't provide DDL/DML statements I haven't been able to test it.

Points to note:

1. Instead of a sub-query you need a full derived query for each part of the union.
2. For any computed order by column you need to compute it in the select and then order by the alias.
3. You need to group by u.[name] not u.[user_id] , you have to group by whatever you are selecting.
4. You had some missing aliases which caused an ambiguous column error.
5. If you want to avg an int column you have to convert it to a decimal of some sort to avoid SQL Server automatically rounding it to an int .

    select results, rating
    from (
      select top 1 u.[name] as results, count(convert(decimal(9,2),m.rating)) rating 
      from users as u
      join movie_rating as m on u.[user_id] = m.[user_id]
      group by u.[name]
      order by rating desc, results asc
    ) X

    union all

    select results, rating
    from (
      select top 1 m.title as results, avg(convert(decimal(9,2),r.rating)) Rating
      from movies as m
      join movie_rating as r on m.movie_id = r.movie_id
      where CONVERT(varchar(7), r.created_at, 121) = '2020-02'
      group by m.title
      order by rating desc, results asc
    ) X;

Answer 2

Per @Dale K, here is revised solution that works.

select a.name as results from (
  select top 1 u.name 
  from users as u
  join movie_rating as m on u.user_id = m.user_id
  group by u.name
  order by count(m.rating) desc, u.name
) a
union all
select title as results from (
  select top 1 m.title 
  from movies as m
  join movie_rating as r on m.movie_id = r.movie_id
  where CONVERT(varchar(7), r.created_at, 121) = '2020-02'
  group by m.title
  order by avg(cast(rating as decimal)) desc, m.title
) b;