mysql求百分比函数

SELECT 
    product_id,
    (SUM(quantity) / (SELECT SUM(quantity) FROM sales) * 100) AS percentage
FROM 
    sales
GROUP BY 
    product_id;

SELECT 
    (SUM(CASE WHEN quantity > 100 THEN quantity ELSE 0 END) / (SELECT SUM(quantity) FROM sales) * 100) AS percentage
FROM 
    sales;

SELECT 
    (SUM(CASE WHEN quantity > 100 THEN CAST(quantity AS FLOAT) ELSE 0 END) / NULLIF((SELECT SUM(CAST(quantity AS FLOAT)) FROM sales), 0) * 100) AS percentage
FROM 
    sales;

CREATE TEMPORARY TABLE total_sales AS 
SELECT SUM(quantity) AS total_quantity FROM sales;

SELECT 
    product_id,
    (SUM(quantity) / total_sales.total_quantity * 100) AS percentage
FROM 
    sales, total_sales
GROUP BY 
    product_id;