Create and populate the example table with these statements:

CREATE TABLE shop (
article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
dealer CHAR(20) DEFAULT '' NOT NULL,
price DOUBLE(16,2) DEFAULT '0.00' NOT NULL,
PRIMARY KEY(article, dealer));

INSERT INTO shop VALUES
(1,'A',3.45),(1,'B',3.99),(2,'A',10.99),(3,'B',1.45),
(3,'C',1.69),(3,'D',1.25),(4,'D',19.95);

The Maximum Value for a Column

SELECT MAX(article) AS article FROM shop;

The Row Holding the Maximum of a Certain Column

Task: Find the number, dealer, and price of the most expensive article.

This is easily done with a subquery:

SELECT article, dealer, price
FROM shop
WHERE price=(SELECT MAX(price) FROM shop);

Maximum of Column per Group

Task: Find the highest price per article.

SELECT article, MAX(price) AS price
FROM shop
GROUP BY article;

The Rows Holding the Group-wise Maximum of a Certain Column

Task: For each article, find the dealer or dealers with the

This problem can be solved with a subquery like this one:

SELECT article, dealer, price
FROM shop s1
WHERE price=(SELECT MAX(s2.price)
FROM shop s2
WHERE s1.article = s2.article);

The preceding example uses a correlated subquery, which can be inefficient (see Section 13.2.10.7, “Correlated Subqueries”). Other possibilities for solving the problem are to use an uncorrelated subquery in the FROM clause or a LEFT JOIN.

Uncorrelated subquery:

SELECT s1.article, dealer, s1.price
FROM shop s1
JOIN (
SELECT article, MAX(price) AS price
FROM shop
GROUP BY article) AS s2
ON s1.article = s2.article AND s1.price = s2.price;

LEFT JOIN:

SELECT s1.article, s1.dealer, s1.price
FROM shop s1
LEFT JOIN shop s2 ON s1.article = s2.article AND s1.price < s2.price
WHERE s2.article IS NULL;