mysql top n per group

SELECT * from (Select Case whenT.province=@prov Then @rownum:=@rownum+1 Else @rownum:=1 EndRowNum, Case whenT.province=@prov Then 0 Else @prov:=T.provinceEndProv, T.* from ( SELECT '110000'Province,1231 Money UNION All SELECT '11

MySQL Group takes the first few records of each group (rank) with group by and order byHttp://www.jb51.net/article/31590.htm--group The data of the row with the maximum (small) value by a fieldThe code is as follows:/**/--Create the table and insert

First, the record of the group to take the top N records: Example: Take the first 2 maximum (small) records1 1. Using subqueries:2SELECT * from Right2 a WHERE2>3(SELECT COUNT (*) from right2 b WHERE b.id=a.id and b.account>a.account)4 ORDER by

Reprint Please specify: theviper http://www.cnblogs.com/TheViperPartially translated from How to select the First/least/max row per group in SQLSome common SQL problems have similar workarounds, such as finding the most recent logs for each program,

The database design may only be based on the current business needs. It may not need high availability, high scaling, and other features at that time, but as the business and user volume increase, the infrastructure is gradually improved. This blog

This article transferred from: HTTPS://WWW.TUICOOL.COM/WX/2EMBFMQObjectiveTalking about MySQL query optimization, I believe you have a collection of artifice: You cannot use SELECT *, do not use null fields, reasonably create an index, select the

Build table:CREATE TABLE Hard (ID INT,AA varchar (50),BB INT,PRIMARY Key (ID))INSERT into hard values (1, ' a ', 9)INSERT into hard values (2, ' a ', 7)INSERT into hard values (3, ' a ', 8)INSERT into hard values (4, ' a ', 6)INSERT into hard values

Build table:CREATE TABLE Hard (ID INT,AA varchar (50),BB INT,PRIMARY Key (ID))INSERT into hard values (1, ' a ', 9)INSERT into hard values (2, ' a ', 7)INSERT into hard values (3, ' a ', 8)INSERT into hard values (4, ' a ', 6)INSERT into hard values

Platform: centos6.4 Mysql:mysql-5.5.33-linux2.6-x86_64.tar.gz One, build LVM, and prepare before installation: #查看当前磁盘的分区 (here alone with a new plus disk for LVM) [Email protected] ~]# fdisk-l/dev/sdbdisk/dev/sdb:128.8 GB, 128849018880 bytes255

(1) Reduce Database Access Static pages are possible Static parts of a dynamic page Some data can be generated as XML or saved as text files Use data caching technology, such as memcached (2)Optimization Detection Method 1. User Experience