performance - How to select a maximum value row in mysql table

Question

I have the following table

Table structure:

CREATE TABLE IF NOT EXISTS `people` ( 
`name` varchar(10) NOT NULL, 
`age` smallint(5) unsigned NOT NULL, 
PRIMARY KEY (`name`) 
) ENGINE=InnoDB DEFAULT CHARSET=latin1; 

Insert some values:

INSERT INTO `people` (`name`, `age`) VALUES 
('bob', 13), 
('john', 25), 
('steve', 8), 
('sue', 13); 

Executed Query:

SELECT MAX(  `age` ) ,  `name` FROM  `people` WHERE 1

Expected Result:

25, John

Generated Result

25, bob

We can achieve this by using this query

SELECT `age`,  `name` FROM  `people` ORDER BY age DESC LIMIT 1

Question 1 : What I made mistake here and why this MAX function is not return the relevant row information?

Question 2: Which one is good to use, to increase performance MAX function or ORDER BY clause?

Answer 1

Question 1 : What I made mistake here and why this MAX function is not return the relevant row information?

You need to read up on the group by clause.

MySQL is being a lot more permissive than it should, introducing confusion in the process. Basically, any column without an aggregate should be included in the group by clause. But MySQL syntactic sugar allows to "forget" columns. When you do, MySQL spits out an arbitrary value from the set that it's grouping by. In your case, the first row in the set is bob, so it returns that.

Question 2: Which one is good to use, to increase performance MAX function or ORDER BY clause?

Your first statement (using max() without a group by) is simply incorrect.

If you want one of the oldest users, order by age desc limit 1 is the correct way to proceed.

If you want all of the oldest users, you need a subselect:

SELECT p.* FROM people p WHERE p.age = (select max(subp.age) from people subp);