I'll start coding with JEE soon. Product environment adopts Oracle WebLogic in Linux, technology adopts EJB3 and JPA. So I'm going to set a development environment in my own computer with them. For iMac installing JDK, Eclipse or Maven wil
I'll start coding with JEE soon. Product environment adopts Oracle + WebLogic in Linux, technology adopts EJB3 and JPA. So I'm going to set a development environment in my own computer with them.
For iMac installing JDK, Eclipse or Maven will not be problem, but installing Oracle seems a impossible mission, now virtualbox become a very good choice.
Install VirtualBox
Download from https://www.virtualbox.org/, nothing special on installing. But it's really a magic tool.
Create a new Virtual Machine for Oracle Linux
You'd better to download a Oracle Linux 7 installer ISO file before starting this step. https://edelivery.oracle.com/linux. You need specify a installer ISO file during the process of creating virtual machine.
1. Name your virtual machine, choose the OS you will install later and set the size of memory.
2. Set the size of virtual machine's "hard disk". Click OK the virtual machine will be created.
You still need change's several basic settings. Select the virtual machine you just created, click "Settings" button on the top of VirtualBox Manager.
1. Specify the installer ISO file which will be installed onto this virtual machine later.
Storage --> Click CD ROM icon on right (Storage Tree) --> Click CD ROM icon on left (Attributes) --> Choose a virtual CD/DVD disk file --> Select the Oracle Linux installer which you downloaded in advance.
2. Enable network connection. This virtual machine will be assigned a IP address you can access from you computer after OS has been installed. For example, you can ssh this virtual machine.
3. All done, click OK.
Install Oracle Linux 7 in this Virtual Machine
1. Select VirtualBox you created former, click "Start" button on top
** Clicking "Left Command Button" can move your mouse cursor out of the installation screen.
2. Software Selection
3. Enable network connection
4. Reboot after complete installation, still need do some basic configurations.
- Enable Kdump
- Set up software update. I select "No, I prefer to register at a later time." because I don't purchase any oracle product...
Rmove OpenJDK
OpenJDK is default JVM in Oracle Linux. I see quite a lot of posts say simply run command "yum remove java*", but I'm not sure if this way is secure because wildcard is used, so it seems not really. I'm going to use software GUI to remove it.
After you login Oracle Linux-->Start menu-->System tools-->Software, search openjdk then remove packages.
Install Oracle JDK
1. Download 64bit jdk archive file
2. Extract it into /usr/lib
3. Add JAVA_HOME variable into /etc/profile. This jvm is enabled for all the users of this vm.
export JAVA_HOME=/usr/lib/jdk-1.8.0-xxx
export PATH=$PATH:$JAVA_HOME/bin

mySqlStringTypesimpactStorageAndPerformanCeaseAsfollows:1)長度,始終使用theSamestoragespace,whatcanbefasterbutlessspace-felfficity.2)varCharisvariable varcharisvariable length,morespace-morespace-morespace-effficitybuteftife buteftife butfority butfority textifforlyslower.3)

mysqlStringTypesIncludeVarChar,文本,char,Enum和set.1)varCharisVersAtileForvariable-lengthStringStringSuptoPuptOuptoPepePecifiedLimit.2)textisidealforlargetStortStorStoverStoverStorageWithoutAutAdefinedLength.3)charlisfixed-lenftenge,for forConsistentDatalikeCodes.4)

MySQLoffersvariousstringdatatypes:1)CHARforfixed-lengthstrings,2)VARCHARforvariable-lengthtext,3)BINARYandVARBINARYforbinarydata,4)BLOBandTEXTforlargedata,and5)ENUMandSETforcontrolledinput.Eachtypehasspecificusesandperformancecharacteristics,sochoose

TograntpermissionstonewMySQLusers,followthesesteps:1)AccessMySQLasauserwithsufficientprivileges,2)CreateanewuserwiththeCREATEUSERcommand,3)UsetheGRANTcommandtospecifypermissionslikeSELECT,INSERT,UPDATE,orALLPRIVILEGESonspecificdatabasesortables,and4)

toadduserInmysqleffect和securly,跟隨台詞:1)USEtheCreateUserStattoDaneWuser,指定thehostandastrongpassword.2)GrantNecterAryAryaryPrivilegesSustherthing privilegesgeStatement,usifementStatement,adheringtotheprinciplelastprefilegege.3)

toaddanewuserwithcomplexpermissionsinmysql,loldtheSesteps:1)創建eTheEserWithCreateuser'newuser'newuser'@''localhost'Indedify'pa ssword';。 2)GrantreadAccesstoalltablesin'mydatabase'withGrantSelectOnMyDatabase.to'newuser'@'localhost';。 3)GrantWriteAccessto'

MySQL中的字符串數據類型包括CHAR、VARCHAR、BINARY、VARBINARY、BLOB、TEXT,排序規則(Collations)決定了字符串的比較和排序方式。 1.CHAR適合固定長度字符串,VARCHAR適合可變長度字符串。 2.BINARY和VARBINARY用於二進制數據,BLOB和TEXT用於大對像數據。 3.排序規則如utf8mb4_unicode_ci忽略大小寫,適合用戶名;utf8mb4_bin區分大小寫,適合需要精確比較的字段。

最佳的MySQLVARCHAR列長度選擇應基於數據分析、考慮未來增長、評估性能影響及字符集需求。 1)分析數據以確定典型長度;2)預留未來擴展空間;3)注意大長度對性能的影響;4)考慮字符集對存儲的影響。通過這些步驟,可以優化數據庫的效率和擴展性。


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