如何使用表头sql将列转换为行

CREATE TABLE employees (
  employee_id INT,
  first_name VARCHAR(50),
  last_name VARCHAR(50),
  salary DECIMAL(10, 2)
);

INSERT INTO employees (employee_id, first_name, last_name, salary)
VALUES (1, 'John', 'Doe', 5000),
       (2, 'Jane', 'Smith', 6000),
       (3, 'Mike', 'Johnson', 7000);

SELECT employee_id, column_name, column_value
FROM employees
UNPIVOT (
  column_value FOR column_name IN (first_name, last_name, salary)
) AS unpivoted_data;

employee_id | column_name | column_value
----------------------------------------
1           | first_name  | John
1           | last_name   | Doe
1           | salary      | 5000
2           | first_name  | Jane
2           | last_name   | Smith
2           | salary      | 6000
3           | first_name  | Mike
3           | last_name   | Johnson
3           | salary      | 7000