有关group by 排序的问题,请进
有这样一个表:tab1
+----+-------+--------+-------+
| id | aa | bb | cc |
+----+-------+--------+-------+
| 1 | 0001 | 1 | 10 |
| 2 | 0001 | 2 | 10 |
| 3 | 0002 | 6 | 10 |
| 4 | 0003 | 5 | 10 |
| 5 | 0003 | 7 | 10 |
| 6 | 0003 | 4 | 10 |
| 7 | 0004 | 3 | 10 |
+----+-------+--------+-------+
用了下列语句:
select aa,bb,sum(cc) as cc from tab1 group by aa order by cc desc,bb desc
输出结果如下:
aa bb cc
======================
0001 1 20
0002 6 10
0003 5 30
0004 3 10
我想要的结果是:
aa bb cc
======================
0001 1 20
0002 6 10
0003 4 30
0004 3 10
也就是说字段bb对应的数据库中最新一条数据的值,这个如何实现???
------解决方案--------------------
试一下
select tab1.aa,tab1.bb,ntab.cc from tab1,(select max(id) as id,sum(cc) as cc from tab1 group by aa) as ntab where tab1.id=ntab.id order by ntab.cc
------解决方案--------------------
楼上的应该是可以出来正确结果。(我没测试,但应该可以)
关于楼主的问题,给你回答下,mysql中group by的时候显示的记录是同group 中最先插入的,也就是最旧的:P呵呵,因此楼主的想法用简单的sql是没办法实现的。

ThesecrettokeepingaPHP-poweredwebsiterunningsmoothlyunderheavyloadinvolvesseveralkeystrategies:1)ImplementopcodecachingwithOPcachetoreducescriptexecutiontime,2)UsedatabasequerycachingwithRedistolessendatabaseload,3)LeverageCDNslikeCloudflareforservin

You should care about DependencyInjection(DI) because it makes your code clearer and easier to maintain. 1) DI makes it more modular by decoupling classes, 2) improves the convenience of testing and code flexibility, 3) Use DI containers to manage complex dependencies, but pay attention to performance impact and circular dependencies, 4) The best practice is to rely on abstract interfaces to achieve loose coupling.

Yes,optimizingaPHPapplicationispossibleandessential.1)ImplementcachingusingAPCutoreducedatabaseload.2)Optimizedatabaseswithindexing,efficientqueries,andconnectionpooling.3)Enhancecodewithbuilt-infunctions,avoidingglobalvariables,andusingopcodecaching

ThekeystrategiestosignificantlyboostPHPapplicationperformanceare:1)UseopcodecachinglikeOPcachetoreduceexecutiontime,2)Optimizedatabaseinteractionswithpreparedstatementsandproperindexing,3)ConfigurewebserverslikeNginxwithPHP-FPMforbetterperformance,4)

APHPDependencyInjectionContainerisatoolthatmanagesclassdependencies,enhancingcodemodularity,testability,andmaintainability.Itactsasacentralhubforcreatingandinjectingdependencies,thusreducingtightcouplingandeasingunittesting.

Select DependencyInjection (DI) for large applications, ServiceLocator is suitable for small projects or prototypes. 1) DI improves the testability and modularity of the code through constructor injection. 2) ServiceLocator obtains services through center registration, which is convenient but may lead to an increase in code coupling.

PHPapplicationscanbeoptimizedforspeedandefficiencyby:1)enablingopcacheinphp.ini,2)usingpreparedstatementswithPDOfordatabasequeries,3)replacingloopswitharray_filterandarray_mapfordataprocessing,4)configuringNginxasareverseproxy,5)implementingcachingwi

PHPemailvalidationinvolvesthreesteps:1)Formatvalidationusingregularexpressionstochecktheemailformat;2)DNSvalidationtoensurethedomainhasavalidMXrecord;3)SMTPvalidation,themostthoroughmethod,whichchecksifthemailboxexistsbyconnectingtotheSMTPserver.Impl


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

SublimeText3 English version
Recommended: Win version, supports code prompts!

MinGW - Minimalist GNU for Windows
This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

Zend Studio 13.0.1
Powerful PHP integrated development environment

Notepad++7.3.1
Easy-to-use and free code editor
