SpirirHost Support Centre: MySQL Reference Manual p.170

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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

170 MySQL Technical Reference for Version 4.0.3 3.5.4 The Rows Holding the Group-wise Maximum of a Certain Field \For each article, nd the dealer(s) with the most expensive price." In ANSI SQL, I'd do it 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 it's best do it in several steps: 1. Get the list of (article,maxprice). 2. For each article get the corresponding rows that have the stored maximum price. This can easily be done with a temporary table: 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 inecient trick that I call 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, of course, be made a bit more ecient by doing the splitting of the concatenated column in the client.

MySQL Reference Manual

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