mysql 按字段分类汇总

CREATE TABLE sales (
    id INT AUTO_INCREMENT PRIMARY KEY,
    product_category VARCHAR(50),
    amount DECIMAL(10, 2),
    sale_date DATE
);

SELECT product_category, SUM(amount) AS total_amount
FROM sales
GROUP BY product_category;

SELECT COALESCE(product_category, 'Unknown') AS category, SUM(amount) AS total_amount
FROM sales
GROUP BY COALESCE(product_category, 'Unknown');

SELECT category, SUM(total_amount) AS total_amount
FROM (
    SELECT product_category AS category, SUM(amount) AS total_amount
    FROM sales
    GROUP BY product_category
) AS subquery
GROUP BY category;

SELECT product_category, SUM(amount) AS total_amount
FROM sales
GROUP BY product_category
ORDER BY total_amount DESC;