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Technical Articles

Database

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

How to Troubleshoot Slow Queries in MongoDB

Enableslowqueryloggingwithdb.setProfilingLevelandanalyzelogsinsystem.profiletoidentifyslowoperations.2.Useexplain("executionStats")todetectinefficiencieslikeCOLLSCANandhighdocsexamined.3.Createcompoundindexesonfilterandsortfields,verifywith

Aug 29, 2025 am 04:10 AM

Can I use variables in Navicat queries?

Yes, Navicat supports the use of variables in queries, depending on the database type and usage scenario. 1. In SQL queries for databases such as MySQL, session variables starting with @ can be defined through SET or SELECTINTO, which can be used to repeatedly reference values, but are only valid in the current connection; 2. In Navicat visual query builder, parameter placeholders (such as $[MyParam]) can be used as variable alternatives, and values ??can be entered at runtime, suitable for non-technical users to reuse queries; 3. In stored procedures or scripts (such as PostgreSQL, SQLServer), local variables (such as variables declared by DECLARE) are required, and their scope is limited to generations.

Aug 29, 2025 am 04:01 AM

How to remove duplicate rows from a table in MySQL

Use the temporary table method to safely deduplicate. First create a temporary table with the same structure, insert the deduplicate data, rename the table and delete the backup; 2. MySQL8.0 can use the ROW_NUMBER() window function to mark duplicate rows, delete rows with a number greater than 1, and retain the first row sorted by the primary key; 3. Old version of MySQL can delete duplicates through self-connection, and retain rows with smaller ids; 4. Adding unique constraints can prevent future duplication. Before the operation, data must be backed up, queries must be tested first, and appropriate methods must be selected based on the MySQL version and primary key conditions. Temporary table method is the safest, and a unique index should be added to prevent duplicate data from appearing again.

Aug 29, 2025 am 03:59 AM