mysql union的用法

SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2;

-- employees 表
CREATE TABLE employees (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    salary DECIMAL(10, 2)
);

-- contractors 表
CREATE TABLE contractors (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    salary DECIMAL(10, 2)
);

-- 插入示例数据
INSERT INTO employees (id, name, salary) VALUES
(1, 'Alice', 50000),
(2, 'Bob', 60000),
(3, 'Charlie', 55000);

INSERT INTO contractors (id, name, salary) VALUES
(1, 'David', 55000),
(2, 'Eve', 65000),
(3, 'Alice', 50000);

SELECT name, salary FROM employees
UNION
SELECT name, salary FROM contractors;

+---------+---------+
| name    | salary  |
+---------+---------+
| Alice   |  50000  |
| Bob     |  60000  |
| Charlie |  55000  |
| David   |  55000  |
| Eve     |  65000  |
+---------+---------+

SELECT name, salary FROM employees
UNION
SELECT name, salary FROM contractors
ORDER BY salary DESC;

SELECT name, salary FROM employees
UNION
SELECT name, salary FROM contractors;