SQL 转换表

SELECT SUM(salary) FROM employees;

SUM(salary)
-----------
30000

SELECT * FROM employees ORDER BY salary DESC;

id |      name      |   salary
---+----------------+----------
 2 | John Doe       |    12000
 3 | Jane Smith     |    10000
 1 | Michael Green  |     8000

SELECT employees.name, departments.department_name
FROM employees
JOIN departments
ON employees.department_id = departments.department_id;

    name    | department_name
------------+-----------------
 John Doe   | Sales
 Jane Smith | HR

SELECT departments.department_name, COUNT(employees.id), AVG(employees.salary)
FROM departments
JOIN employees
ON departments.department_id = employees.department_id
GROUP BY departments.department_name;

department_name | count |        avg
-----------------+-------+---------------------
 Sales           |     1 |                12000
 HR              |     2 | 9500.00000000000000

SELECT id, name, TO_CHAR(date_field, 'YYYY-MM-DD') AS formatted_date
FROM table_name;

id |      name      | formatted_date
---+----------------+----------------
 1 | John Doe       |     2022-01-01
 2 | Jane Smith     |     2022-02-01