mysql实现多张表合并

-- users表结构
CREATE TABLE users (
    id INT PRIMARY KEY,
    name VARCHAR(50),
    email VARCHAR(50)
);

-- orders表结构
CREATE TABLE orders (
    id INT PRIMARY KEY,
    user_id INT,
    product VARCHAR(50),
    amount DECIMAL(10, 2)
);

-- 插入示例数据
INSERT INTO users (id, name, email) VALUES
(1, 'Alice', 'alice@example.com'),
(2, 'Bob', 'bob@example.com');

INSERT INTO orders (id, user_id, product, amount) VALUES
(1, 1, 'Product A', 100.00),
(2, 1, 'Product B', 50.00),
(3, 2, 'Product C', 75.00);

SELECT users.name, orders.product, orders.amount
FROM users
INNER JOIN orders ON users.id = orders.user_id;

SELECT users.name, orders.product, orders.amount
FROM users
LEFT JOIN orders ON users.id = orders.user_id;

SELECT users.name, orders.product, orders.amount
FROM users
RIGHT JOIN orders ON users.id = orders.user_id;

SELECT name, (SELECT SUM(amount) FROM orders WHERE user_id = users.id) AS total_amount
FROM users;

SELECT name, 'User' AS type FROM users
UNION
SELECT product, 'Order' AS type FROM orders;