SELECT 列1, 列2, ..., 聚合函数(列或表达式)
FROM 表名
GROUP BY 列1, 列2, ...

CREATE TABLE employee (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  department VARCHAR(100),
  salary INT
);

INSERT INTO employee (id, name, department, salary)
VALUES 
  (1, 'Alice', 'HR', 5000),
  (2, 'Bob', 'HR', 6000),
  (3, 'Charlie', 'Finance', 7000),
  (4, 'David', 'Finance', 8000),
  (5, 'Eve', 'IT', 9000),
  (6, 'Frank', 'IT', 10000);

SELECT department, SUM(salary) AS total_salary, AVG(salary) AS average_salary, COUNT(*) AS employee_count
FROM employee
GROUP BY department;

department | total_salary | average_salary | employee_count
-----------|--------------|----------------|----------------
HR         | 11000        | 5500           | 2
Finance    | 15000        | 7500           | 2
IT         | 19000        | 9500           | 2

SELECT department, SUM(salary) AS total_salary
FROM employee
GROUP BY department
HAVING SUM(salary) > 12000;

department | total_salary
-----------|--------------
Finance    | 15000
IT         | 19000