mysql - 执行具有完整性约束的 'subset' 关系的最佳方法是什么

Question

例如，给定 3 个表:

• 腹足动物
• 蜗牛
• 鼻涕虫

假设我们想要强制执行

1. “腹足动物”中的每一行在“蜗牛”或“蛞蝓”(但不是两者)中都有对应的一行
2. “slug”中的每一行在“gastropod”中恰好对应一行
3. “snail”中的每一行在“gastropod”中恰好对应一行

设置架构以强制执行这些约束的最佳方式是什么？

我已经为 postgres 提供了一个可能的答案，我对 postgres 和 Oracle 的解决方案特别感兴趣，但也有兴趣查看其他 RDBMS 的解决方案

编辑
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Answer 1

我自己的 postgres 解决方案(但我不知道这是否是最好的方法):

枚举:

create type gastropod_type as enum ('slug', 'snail');

表和约束:

create table gastropod(
  gastropod_id serial unique,
  gastropod_type gastropod_type,
  slug_gastropod_id integer,
  snail_gastropod_id integer,
  average_length numeric,
  primary key(gastropod_id, gastropod_type),
  check( (case when slug_gastropod_id is null then 0 else 1 end)+
         (case when snail_gastropod_id is null then 0 else 1 end)=1) );

create table slug(
  gastropod_id integer unique,
  gastropod_type gastropod_type check (gastropod_type='slug'),
  is_mantle_visible boolean,
  primary key(gastropod_id, gastropod_type),
  foreign key(gastropod_id, gastropod_type) 
    references gastropod deferrable initially deferred );

create table snail(
  gastropod_id integer unique,
  gastropod_type gastropod_type check (gastropod_type='snail'),
  average_shell_volume numeric,
  primary key(gastropod_id, gastropod_type),
  foreign key(gastropod_id, gastropod_type)
    references gastropod deferrable initially deferred );

alter table gastropod 
add foreign key(slug_gastropod_id, gastropod_type) 
references slug deferrable initially deferred;

alter table gastropod 
add foreign key(snail_gastropod_id, gastropod_type) 
references snail deferrable initially deferred;

测试:

insert into gastropod(gastropod_type, slug_gastropod_id, average_length)
values ('slug', currval('gastropod_gastropod_id_seq'), 100);

insert into slug(gastropod_id, gastropod_type, is_mantle_visible)
values (currval('gastropod_gastropod_id_seq'), 'slug', true);

select gastropod_id, gastropod_type, average_length, is_mantle_visible
from gastropod left outer join slug using(gastropod_id, gastropod_type) 
               left outer join snail using(gastropod_id, gastropod_type);

 gastropod_id | gastropod_type | average_length | is_mantle_visible
--------------+----------------+----------------+-------------------
            1 | slug           |            100 | t                 
(1 row)