如何在SQL中使用group by？

SELECT 列1, 列2, ..., 聚合函数(列)
FROM 表名
GROUP BY 列1, 列2, ...

SELECT department, SUM(sales) AS total_sales
FROM sales_table
GROUP BY department;

SELECT city, COUNT(order_id) AS order_count
FROM orders_table
GROUP BY city;

SELECT category, AVG(price) AS avg_price
FROM products_table
GROUP BY category;

SELECT salesperson, MONTH(sale_date) AS month, SUM(amount) AS total_sales
FROM sales_table
GROUP BY salesperson, MONTH(sale_date);