mysql - 坚持使用 MySQL 查询

Question

我有一个表架构为

create table Location(
id int primary key,
city varchar(255),
state varchar(100),
country varchar(255)
);
create table Person( 
id int primary key,
name varchar(100)
);
create table Photographer(
id int primary key references Person(id) on update cascade on delete cascade,
livesIn int not null references Location(id) on update cascade on delete no action
);
create table Specialty(
photographer int references Photographer(id) on update cascade on delete cascade,
type enum('portrait','landscape','sport'),
primary key(photographer, type)
);
create table Photo(
id int primary key,
takenAt timestamp not null,
takenBy int references Photographer(id) on update cascade on delete no action,
photographedAt int references Location(id) on update cascade on delete no action
);
create table Appearance(
  shows int references Person(id) on update cascade on delete cascade,
isShownIn int references Photo(id) on update cascade on delete cascade,
primary key(shows, isShownIn)
);

我遇到了两个问题:

1) 仅显示居住在同一地点的摄影师的照片。每张照片列出一次。也就是说，照片必须有摄影师，他们都需要住在同一个地方。

2) 地点的每张照片都由马萨诸塞州任何照片中未出现的摄影师拍摄？对于每个位置仅显示城市，并且每个位置仅显示一次。

我的尝试:1)

SELECT ph.id, ph.takenAt, ph.takenBy, ph.photographedAt FROM 
(SELECT * FROM Photo p, Appearance ap WHERE p.id = ap.isShownIn 
HAVING ap.shows IN (SELECT person.id FROM Person,Photographer WHERE person.id
photographer.id)) ph
WHERE ph.photographedAt = (SELECT location.id FROM location WHERE location.id = 
(SELECT livesIn FROM Photographer WHERE id = ph.takenBy))

2)

select distinct city from location where location.id in (
select photographedAt from photo, (select * from appearance where appearance.shows in
(select photographer.id from photographer)) ph
where photo.id = ph.isShownIn )
and location.state <> 'Massachusetts'

任何人都可以帮助创建这些查询吗？？

Answer 1

您的查询是“列出具有属性 X 和 Y 的单个项目，其中 X 和 Y 在不同的表中” 的两种查询。

这些类型的问题通常使用带有 EXISTS 和 NOT EXISTS 的相关子查询来解决。

使用 EXISTS 处理“每个项目只显示一次” 部分。否则，您需要将分组与复杂的联接结合使用，这很快就会变得困惑。

问题 1 要求:

[...] photos must have persons that are photographers, and they all need to live in the same place.

请注意，此定义并没有说“如果照片中也包含其他人，则不要显示照片”。如果这就是您的真正意思，那么您可以从下面的 SQL 中得出结论并在下次编写更好的定义。 ;)

SELECT
  *
FROM
  Photo p
WHERE
  EXISTS (
    -- ...that has at least one appearance of a photographer
    SELECT 
      1 
    FROM
      Appearance              a 
      INNER JOIN Photographer r ON r.id = a.shows
      INNER JOIN Location     l ON l.id = r.livesIn
    WHERE
      a.isShownIn = p.id
      -- AND l.id = <optional location filter would go here>
      AND NOT EXISTS (
        -- ...that does not have an appearance of a photographer from 
        --    some place else
        SELECT 
          1 
        FROM
          Appearance              a1 
          INNER JOIN Photographer r1 ON r1.id = a1.shows
          INNER JOIN Location     l1 ON l1.id = r1.livesIn
        WHERE
          a1.isShownIn = p.Id
          AND l1.id <> l.id
      )
  )

第二题读

[...] locations that have the property that every photo in the location was taken by a photographer who is not shown in any photo in Massachusetts? For each location show only the city, and show each location only once.

相应的 SQL 看起来像:

SELECT
  city
FROM
  Location l
WHERE
  NOT EXISTS (
    -- ...a photo at this location taken by a photographer who makes 
    --    an apperance on another photo which which was taken in Massachusetts
    SELECT
      1
    FROM
      Photo                    p
      INNER JOIN Photographer  r ON r.id = p.takenBy
      INNER JOIN Appearance    a ON a.shows = r.id
      INNER JOIN Photo        p1 ON p1.id = a.isShownIn
    WHERE
      p.photographedAt = l.Id
      AND p1.photographedAt = <the location id of Massachusetts>
  )