查询 tables 中 FK 在 junction table 中引用的其他字段

Question

我有一个 "junction" table (recipe_ingredients)，我用它来处理数据库中的多对多关系。 table 中的每个字段都是对另一个 table 的 PK 的引用：recipe_id、ingredient_id、quantity_id 和 measure_id。这些是 metadata、ingredients、quantities 和 measurements table 的 PK。除了 metadata table，所有这些 table 都只有两个字段：PK，以及与该 PK 关联的名称或号码。

我正在尝试查询 recipe_ingredients 具有给定 recipe_id 的所有行...但我不想在每一行中显示具有 recipe_id 的主键在 table.

中显示与该 PK 关联的 name/number

所以不是查询 returns 这个：

recipe_id | ingredient_id | quantity_id | measure_id
----------+---------------+-------------+-----------
1         | 10            | 2           | 3
----------+---------------+-------------+-----------
1         | 12            | 2           | 3
----------+---------------+-------------+-----------
1         | 13            | 5           | 6
----------+---------------+-------------+-----------
...

我正在寻找 returns 类似这样的查询：

recipe_id | ingredient_name | quantity_num | measure_num
----------+-----------------+--------------+------------
1         | Ground cayenne  | 1/2          | tsp
----------+-----------------+--------------+------------
1         | Ground paprika  | 1/2          | tsp
----------+-----------------+--------------+------------
1         | Olive oil       | 1            | tbsp
----------+-----------------+--------------+------------
...

我刚开始学习SQL，所以我只知道如何对单个table进行简单的查询。我什至不知道从哪里开始这个查询，只是我可能需要一种 join 语句。我可以写什么查询来实现这个？

我在 Debian 上使用 sqlite3。

recipe_ingredients"junction"table:

CREATE TABLE recipe_ingredients (
    recipe_id               int,
    ingredient_id           int,
    quantity_id             int,
    measure_id              int,
    primary key (recipe_id, ingredient_id),
    foreign key (recipe_id)
            references metadata (recipe_id)
                    on update restrict
                    on delete restrict,
    foreign key (ingredient_id)
            references ingredients (ingredient_id)
                    on update restrict
                    on delete restrict,
    foreign key (quantity_id)
            references quantities (quantity_id)
                    on update restrict
                    on delete restrict,
    foreign key (measure_id)
            references measurements (measure_id)
                    on update restrict
                    on delete restrict
);

这些是结点 table:

引用的外部 table

create table if not exists ingredients (
    ingredient_id           integer         primary key,
    ingredient_name         text            not null
);

create table if not exists quantities (
    quantity_id             integer         primary key,
    quantity_num            int             not null
);

create table if not exists measurements (
    measure_id              integer         primary key,
    measure_name            text            not null
);

create table if not exists metadata (
    recipe_id               integer         primary key,
    recipe_name             text            not null,
    course_id               int,
    cuisine_id              int,
    servings                int,
    prep_time               int,
    cook_time               int,
    total_time              int,
    foreign key (course_id)
            references courses (course_id)
                    on update restrict
                    on delete restrict,
    foreign key (cuisine_id)
            references cuisine (cuisine_id)
                    on update cascade
                    on delete cascade
);

Answer 1

您可以 join 连接点 table 与每个相关的 table 像这样：

select
    ri.recipe_id,
    i.ingredient_name,
    q.quantity_num,
    m.measure_num
from recipe_ingredients ri
inner join ingredients i  on i.ingredient_id = ri.ingredient_id
inner join quantities q   on q.quantity_id = ri.quantity_id
inner noin measurements m on m.measure_id = ri.measure_id
where ri.recipe_id = ?

问号(?)代表您要查找的recipe_id。

查询 tables 中 FK 在 junction table 中引用的其他字段

Query other fields in tables referenced by FK in junction table

sql

sqlite

join

junction-table