如何使用MySQL构建一个多公司/分支机构会计系统表结构以支持多个实体的财务管理？

CREATE TABLE companies (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(50) NOT NULL,
  reGIStration_number VARCHAR(50) NOT NULL
);

CREATE TABLE branches (
  id INT PRIMARY KEY AUTO_INCREMENT,
  company_id INT NOT NULL,
  name VARCHAR(50) NOT NULL,
  address VARCHAR(100) NOT NULL,
  FOREIGN KEY (company_id) REFERENCES companies(id)
);

CREATE TABLE accounts (
  id INT PRIMARY KEY AUTO_INCREMENT,
  branch_id INT NOT NULL,
  name VARCHAR(50) NOT NULL,
  balance DECIMAL(10, 2) DEFAULT 0,
  FOREIGN KEY (branch_id) REFERENCES branches(id)
);

CREATE TABLE transactions (
  id INT PRIMARY KEY AUTO_INCREMENT,
  account_id INT NOT NULL,
  date DATE NOT NULL,
  type ENUM('收入', '支出') NOT NULL,
  amount DECIMAL(10, 2) NOT NULL,
  FOREIGN KEY (account_id) REFERENCES accounts(id)
);

INSERT INTO companies (name, registration_number) VALUES
  ('公司A', '123456'),
  ('公司B', '789012');

INSERT INTO branches (company_id, name, address) VALUES
  (1, '分支机构A1', '地址A1'),
  (1, '分支机构A2', '地址A2'),
  (2, '分支机构B1', '地址B1');

INSERT INTO accounts (branch_id, name, balance) VALUES
  (1, '账户A11', 1000),
  (1, '账户A12', 2000),
  (2, '账户A21', 1500),
  (3, '账户B11', 3000);

INSERT INTO transactions (account_id, date, type, amount) VALUES
  (1, '2021-01-01', '收入', 500),
  (1, '2021-01-02', '支出', 200),
  (2, '2021-01-03', '收入', 1000),
  (3, '2021-01-04', '支出', 500),
  (4, '2021-01-05', '收入', 800);