select 10 rows per day with order

Question

i have a db with records with date (timestamp) i need to select 10 records for each day (there are many more per day) and order them by few columns...

how should that qu

Answer 1

old question, but I found magnificient answer ( not my own ) using session variables.

Considering table

CREATE TABLE `report` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`reportDate` int(11) DEFAULT NULL,
`count` int(11) DEFAULT NULL,
`parameter` varchar(100) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `INDEX1` (`reportDate`,`parameter`,`count`)
) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8;

Following query will select top 10 parameter per day based on their counts on that day

SELECT parameter, reportDate, count
FROM
    (SELECT parameter, 
             reportDate, 
             count, 
             @reportDate_rank := IF(@current_reportDate = reportDate,@reportDate_rank + 1, 1) AS reportDate_rank,
             @current_reportDate := reportDate 
    FROM report
    ORDER BY reportDate, count DESC
    ) dateRanked
WHERE reportDate_rank <= 10;