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Technical Articles

Database

How to create a SPFILE from a PFILE in Oracle

TocreateanSPFILEfromaPFILE,firstensureavalidPFILEexistsinthedefaultlocationorspecifyacustompath.2.ConnecttothedatabaseusingSQL*PluswithSYSDBAprivilegesviasqlplus/assysdba.3.RunCREATESPFILEFROMPFILE;togeneratetheSPFILEfromthePFILEusingdefaultpaths,ors

Aug 29, 2025 am 08:32 AM

How to use LEAD and LAG functions in SQL?

LEAD and LAG functions are used to access the data of the previous or next row in the result set without self-concatenation; 1. LAG (column,offset,default) gets the value of the previous row, offset specifies the number of traceback rows, default is 1, default is the default value when there is no previous value; 2. LEAD (column,offset,default) gets the value of the subsequent row, the parameters are the same as LAG; 3. Both must be used in conjunction with the OVER() clause, ORDERBY defines the row order, and optional PARTITIONBY can be partitioned by group; 4. In the example, the difference between daily sales and previous days is compared by LAG and LEAD; 5. The offset and default can be set to process edges.

Aug 29, 2025 am 08:01 AM

How to install Oracle Database

Ensure that the system meets prerequisites such as hardware, operating system and swap space; 2. Install the required software packages, create oracle users and groups, configure kernel parameters and shell restrictions; 3. Download and decompress the Oracle database software to the specified directory; 4. Run runInstaller as oracle user to start graphical or silent installation, select the installation type and execute the root script; 5. Use DBCA to create the database silently and set the instance parameters; 6. Configure ORACLE_BASE, ORACLE_HOME, ORACLE_SID and PATH environment variables; 7. Start the instance through sqlplus/assysdba and verify the database status, confirm that the installation is successful,

Aug 29, 2025 am 07:51 AM

What is the GETDEL command introduced in Redis 6.2?

GETDEL was introduced in Redis 6.2 to atomically obtain and delete string keys. 1. It combines the GET and DEL that originally required two operations into one to avoid concurrent interference; 2. Return the value and delete it if the key exists, otherwise it returns nil; 3. Applicable to scenes such as one-time tokens, light queues, and deletion after fetching; 4. Only support string types, efficient operation and atomicity, and is suitable for use in high-concurrency environments.

Aug 29, 2025 am 07:35 AM

How to use window functions in SQL?

WindowfunctionsinSQLenablecalculationsacrossrelatedrowswithoutcollapsingresults,makingthemidealforranking,runningtotals,movingaverages,androwcomparisons.1.Thebasicsyntaxisfunction_name(expression)OVER([PARTITIONBY][ORDERBY][frame_clause]),wherePARTIT

Aug 29, 2025 am 07:29 AM

sql Window Functions

How to manage events in Navicat?

The key to managing events in Navicat is to be familiar with the process and pay attention to details. 1. To create an event, you need to confirm that the database engine supports event scheduler (such as MySQL needs to enable EventScheduler), create new events through the Navicat graphical interface, set the name, execution time, and write SQL scripts to save and enable it; 2. Modify events to adjust the schedule time or SQL content in the editing interface, and can be manually run or viewed during debugging or check the log and process list; 3. Delete or disable events can be completed by right-clicking operations. Dependency needs to be confirmed before deletion to avoid affecting the system operation. Master the above steps to efficiently manage database events.

Aug 29, 2025 am 07:06 AM

What are the key metrics to monitor for a healthy Redis instance?

TokeepaRedisinstancehealthy,monitorkeymetricsinthefollowingorder:1.Memoryusage,trackingused_memoryandused_memory_rsswhileapproachingsystemRAMlimits,andmanagingitviamaxmemory,evictionpolicies,efficientdatastructures,andcompression;2.CPUutilization,mon

Aug 29, 2025 am 06:38 AM

redis Monitoring indicators

How do you handle errors in SQL?

UseTRY-CATCHblocksinsupporteddatabaseslikeSQLServertohandleerrorswithinstoredproceduresandenabletransactionrollback;2.ValidatedatabeforeexecutionbycheckingconditionssuchasrecordexistenceorusingMERGEstatementstopreventconflicts;3.Applyproperconstraint

Aug 29, 2025 am 06:37 AM

How to change user password in phpMyAdmin

LogintophpMyAdminwithadministrativeprivileges.2.Navigatetothe"Useraccounts"or"Privileges"tab.3.Locatethetargetuserandclick"Editprivileges".4.Inthe"Changepassword"section,enteranewpasswordorusethegenerator.5.Sel

Aug 29, 2025 am 06:11 AM

How to set up two-factor authentication in phpMyAdmin

phpMyAdmindoesnotsupportnativetwo-factorauthentication,but2FAcanbeimplementedexternallyusingareverseproxy.1.UseNginxwithGoogleAuthenticatorviaPAM:installNginx,apache2-utils,andlibpam-google-authenticator;2.SetupGoogleAuthenticatorfortheuserandscanthe

Aug 29, 2025 am 05:50 AM

How to find duplicate values in a table in MySQL

To find duplicate values ??in MySQL table, you should use the GROUPBY and HAVING clauses; 1. Use SELECTemail,COUNT()AScountFROMusersGROUPBYemailHAVINGCOUNT()>1; to find duplicate mailboxes; 2. When expanding to multiple columns, use SELECTfirst_name,last_name,COUNT()AScountFROMusersGROUPBYfirst_name,last_nameHAVINGCOUNT()>1; to find duplicates based on multiple fields; 3. When looking for completely duplicate rows, all columns are performed

Aug 29, 2025 am 05:17 AM

How does concurrency control work in SQL databases?

ConcurrencycontrolinSQLdatabasesworksbyusingisolationlevels,lockingmechanisms,MVCC,andconflictdetectiontoensuredataconsistencyandhighperformance.1.Isolationlevels—ReadUncommitted,ReadCommitted,RepeatableRead,andSerializable—definehowtransactionsinter

Aug 29, 2025 am 05:11 AM

How to convert a string to an integer in SQL

To convert a string to an integer, you should choose the appropriate method according to the database system: use the CAST() or CONVERT() function, where CAST('123'ASINTEGER) is a standard and portable writing method, suitable for PostgreSQL, MySQL, SQLServer, SQLite, and Oracle; SQLServer also supports CONVERT(INT,'123') and the safer TRY_CAST('123abc'ASINT) (returns NULL instead of an error when the conversion fails); MySQL uses CAST('123'ASSIGNED) or CONVERT('123',SIGNED),

Aug 29, 2025 am 05:00 AM

How to use the CASE statement in MySQL?

There are two forms of CASE statements in MySQL: search type CASE and simple type CASE, among which search type is more commonly used; search type returns the corresponding results through the WHEN clause specified conditions, which are suitable for clauses such as SELECT, UPDATE, ORDERBY, etc., and can be used for data classification, custom sorting and condition update; simple type matches expressions with multiple values ??one by one and returns the result; CASE must end with END, ELSE is optional, but it is recommended to avoid NULL values; combined with aggregate functions, conditional statistics can be implemented, such as group counting with SUM (CASEWHEN...), thereby improving SQL's flexibility and functionality in data conversion and report generation.

Aug 29, 2025 am 04:33 AM