我有一个包含四个表的PostgreSQL数据库：用户、国家、城市和街道。用户表包含有关用户的信息，包括他们的姓名、级别（可以是“国家”、“城市”或“街道”）以及与他们所属的“国家”、“城市”和“街道”的ID相对应的id。
表格结构：

CREATE TABLE "user" (
  id INT PRIMARY KEY,
  name VARCHAR(255) NOT NULL,
  level VARCHAR(10) NOT NULL, --ENUM('Country', 'City', 'Street')
  id_country INT NULL,
  id_city INT NULL,
  id_street INT NULL,
  FOREIGN KEY (id_country) REFERENCES Country(id) ON UPDATE CASCADE ON DELETE CASCADE,
  FOREIGN KEY (id_city) REFERENCES City(id) ON UPDATE CASCADE ON DELETE CASCADE,
  FOREIGN KEY (id_street) REFERENCES Street(id) ON UPDATE CASCADE ON DELETE CASCADE
);

x

CREATE TABLE Country (
  id INT PRIMARY KEY,
  name VARCHAR(255) NOT NULL,
  code INT NOT NULL
);

CREATE TABLE City (
  id INT PRIMARY KEY,
  name VARCHAR(255) NOT NULL,
  code INT NOT NULL,
  id_country INT NOT NULL,
  FOREIGN KEY (id_country) REFERENCES Country(id) ON UPDATE CASCADE ON DELETE CASCADE
);

CREATE TABLE Street (
  id INT PRIMARY KEY,
  name VARCHAR(255) NOT NULL,
  code INT NOT NULL,
  id_city INT NOT NULL,
  FOREIGN KEY (id_city) REFERENCES City(id) ON UPDATE CASCADE ON DELETE CASCADE
);

的数据
我想在User表和其他三个表之间建立适当的关系，这样我就可以根据用户的级别直接访问相应的“Country”、“City”或“Street”。我目前的方法包括为每种情况添加三个单独的列（id_country、id_city、id_street）和三个连接操作，这似乎是重复的，不是理想的设计。
我的用例的一个例子是：

switch (user.level) {
  case "Country":
    query = ' SELECT * from "user" AS u
              INNER JOIN country c ON u.id_country = c.id '
    break;

  case "City":
    query = ' SELECT * from "user" AS u
              INNER JOIN city c ON u.id_city = c.id '
    break;

  case "Street":
    query = ' SELECT * from "user" AS u
              INNER JOIN street s ON u.id_street = s.id '
    break;
}

型
是否有一种更有效、更简洁的方法来在User表中表示这些关系，同时保持数据完整性并遵守标准数据库设计原则？
我想到了使用这样的复合外键

CREATE TABLE "user" (
  id INT PRIMARY KEY,
  name VARCHAR(255) NOT NULL,
  location_id INT NOT NULL,
  location_type VARCHAR(10) NOT NULL, --ENUM('Country', 'City', 'Street')
  FOREIGN KEY (location_id, location_type) REFERENCES Country(id, 'Country' )
    ON UPDATE CASCADE
    ON DELETE CASCADE,
  FOREIGN KEY (location_id, location_type) REFERENCES City(id, 'City' )
    ON UPDATE CASCADE
    ON DELETE CASCADE,
  FOREIGN KEY (location_id, location_type) REFERENCES Street(id, 'Street' )
    ON UPDATE CASCADE
    ON DELETE CASCADE
);

型
但是，SQL不接受静态值作为引用。我没有SQL的高级知识。
如有任何改进数据库设计的建议或替代办法，将不胜感激。谢谢你，谢谢