Postgresql在插入/更新中为完整性约束创建触发器

Question

我在 Postgresql 的数据库中有这些表：

create table company (
  id bigint generated always as identity primary key,
  name text not null
);

create table employee (
  id bigint generated always as identity primary key,
  name text not null,
  company_id bigint not null references company(id)
);

create table manager_employee(
  id bigint generated always as identity primary key,
  manager_id bigint not null references employee(id),
  employee_id bigint not null references employee(id)
);
create unique index ux1_manager_employee on manager_employee(manager_id, employee_id);
alter table manager_employee add constraint ck1_manager_employee check (manager_id != employee_id);

我想确定当我在manager_employee 表中插入/更新值时，manager_id 和employee_id 都属于同一公司，同一company_id。

我想我必须使用触发器来确保这个条件，我该如何创建它？

谢谢

Answer 1

你可以通过约束来做到这一点：

ALTER TABLE manager_employee ADD company_id bigint;

UPDATE manager_employee me
SET company_id = e.company_id
FROM employee e
WHERE me.employee_id = e.id;

ALTER TABLE manager_employee ALTER company_id SET NOT NULL;

ALTER TABLE employee ADD UNIQUE (company_id, id);

ALTER TABLE manager_employee ADD FOREIGN_KEY (company_id, manager_id)
   REFERENCES employee(company_id, id);

ALTER TABLE manager_employee ADD FOREIGN_KEY (company_id, employee_id)
   REFERENCES employee(company_id, id);

唯一约束与新列一样冗余，但作为外键约束的目标是必需的。