Question

I’ve got a little problem with correct query and hope you can help me. My testing tables structures are as follow:

CREATE TABLE IF NOT EXISTS `users` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`id`),
) ;

CREATE TABLE IF NOT EXISTS `user_throws` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,
  `length` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`,`user_id`),
) ;

The relations between them is many to one (a user can have many throws). The thing is I need to make a somekind ranking page for all users let’s say top 100 throwers. So I need a query result to be:

1. Filtered by users so only the users who have any throws and the length of throw is greater than 0 is correct record.
2. Filtered by duplicates so only unique users appear on the list (GROUP BY I suppose).
3. Sorted by length of throws so only the best (greatest) result will be appended.

For that purpose I wrote the query:

SELECT  `user_throws`.`length` , `users` . * 
FROM  `users` 
JOIN  `user_throws` ON (  `user_throws`.`user_id` =  `users`.`id` ) 
WHERE  `user_throws`.`length` >  '0'
GROUP BY  `users`.`id` 
ORDER BY  `user_throws`.`length` DESC 

But the problem is results are not being sorted by longest throw. It filters the throws with length greater than 0 and displays unique users but the length appended does not correspond with desired sorting. I found out that the length value is the value of throw with lowest user_throws.id that is associated with the user. How should the correct query look like?

Answer 1

Try:

SELECT longthrow,id,name FROM (
SELECT max(t.length) longthrow,u.id,u.name
FROM users u, user_throws t
WHERE u.id=t.user_id
 AND t.length>0
GROUP BY u.id
) ORDER BY longthrow DESC

Which should give you the longest throw of each user, sorted by furthest throw first, shortest last – think that’s what you wanted 😉

And I should add before the comments show up, it’s better to start it with:

SELECT max(t.length) longthrow,u.id,u.name

Than:

SELECT max(t.length) longthrow,u.*