Пак Max проблем в MySQL :)

use test ;

drop table if exists Sklad;

create table Sklad (

   Id int(5) not null auto_increment,

   Sklad int(5),

   IdSelf int(5),

   Cnt double(5,0),

   primary key (Id))

   type=MyISAM;



insert  into Sklad values 

(1, 1, 1, '20'), 

(2, 2, 2, '5'), 

(3, 1, 1, '15');



SELECT MAX( sklad.Id ) AS MAX_OF_Id,   sklad.Sklad,  sklad.IdSelf,  sklad.Cnt

FROM sklad

GROUP BY sklad.IdSelf;

Резултатът е:
Id Sklad IdSelf Cnt
2 2 2 5
3 1 1 20
А редът 3,1,1 трябва да има Cnt=15.
Моля, пишете къде ми е грешката в този простичък sql!

Допълнение: Верията която използвам е MySQL 4.0.14.

От MySQL tutorial:

The Rows Holding the Group-wise Maximum of a Certain Field
``For each article, find the dealer or dealers with the most expensive price.''

In standard SQL (and as of MySQL 4.1), the problem can be solved with a subquery like this:

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

In MySQL versions prior to 4.1, it's best do it in several steps:

Get the list of (article,maxprice) pairs.
For each article, get the corresponding rows that have the stored maximum price.
This can easily be done with a temporary table and a join:

CREATE TEMPORARY TABLE tmp (
article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
price DOUBLE(16,2) DEFAULT '0.00' NOT NULL);

LOCK TABLES shop READ;

INSERT INTO tmp SELECT article, MAX(price) FROM shop GROUP BY article;

SELECT shop.article, dealer, shop.price FROM shop, tmp
WHERE shop.article=tmp.article AND shop.price=tmp.price;

UNLOCK TABLES;

DROP TABLE tmp;

If you don't use a TEMPORARY table, you must also lock the tmp table.

``Can it be done with a single query?''

Yes, but only by using a quite inefficient trick called the ``MAX-CONCAT trick'':

SELECT article,
SUBSTRING( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 7) AS dealer,
0.00+LEFT( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 6) AS price
FROM shop
GROUP BY article;

+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0001 | B | 3.99 |
| 0002 | A | 10.99 |
| 0003 | C | 1.69 |
| 0004 | D | 19.95 |
+---------+--------+-------+

The last example can be made a bit more efficient by doing the splitting of the concatenated column in the client.