mysql 行列换

CREATE TABLE sales (
    product_id INT,
    sale_date DATE,
    quantity INT,
    price DECIMAL(10, 2)
);

SELECT 
    product_id,
    SUM(CASE WHEN MONTH(sale_date) = 1 THEN quantity * price ELSE 0 END) AS Jan_Sales,
    SUM(CASE WHEN MONTH(sale_date) = 2 THEN quantity * price ELSE 0 END) AS Feb_Sales,
    SUM(CASE WHEN MONTH(sale_date) = 3 THEN quantity * price ELSE 0 END) AS Mar_Sales
FROM 
    sales
GROUP BY 
    product_id;

SELECT 
    product_id,
    (SELECT SUM(quantity * price) FROM sales s2 WHERE s2.product_id = s1.product_id AND MONTH(s2.sale_date) = 1) AS Jan_Sales,
    (SELECT SUM(quantity * price) FROM sales s2 WHERE s2.product_id = s1.product_id AND MONTH(s2.sale_date) = 2) AS Feb_Sales,
    (SELECT SUM(quantity * price) FROM sales s2 WHERE s2.product_id = s1.product_id AND MONTH(s2.sale_date) = 3) AS Mar_Sales
FROM 
    sales s1
GROUP BY 
    product_id;