MySQL是很多企業和網站常用的一種數據庫，它具備高性能、可靠性和易用性的特點。在使用MySQL時，有時候需要查詢每個類別的前n條數據。下面我們分別介紹如何實現這些查詢：

1.查詢每個類別的前n條數據

SELECT *
FROM (
SELECT *,
ROW_NUMBER()
OVER (PARTITION BY category_id
ORDER BY order_no ASC) AS row_num
FROM product
) AS temp
WHERE row_num <= n;

2.查詢每個類別包含的記錄數

SELECT category_id, COUNT(*) AS count
FROM product
GROUP BY category_id;

3.查詢每個類別的平均價格

SELECT category_id, AVG(price) AS avg_price
FROM product
GROUP BY category_id;

4.查詢每個類別的最大和最小價格

SELECT category_id, MIN(price) AS min_price, MAX(price) AS max_price
FROM product
GROUP BY category_id;

總之，MySQL提供了很多查詢每個類別的前n條數據的方法，開發人員需要根據實際業務需求選擇合適的方法來進行查詢。