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Technical Articles

Database

Optimizing SQL ORDER BY for Query Performance

To optimize the performance of ORDERBY in SQL, you must first understand its execution mechanism and make rational use of index and query structure. When the sorting field has no index, the database will trigger "filesort", consuming a lot of resources; therefore, direct sorting of large tables should be avoided and the amount of sorted data should be reduced through WHERE conditions. Secondly, establishing a matching index for sorting fields can greatly speed up queries, such as creating reverse order indexes in MySQL 8.0 to improve efficiency. In addition, deep paging (such as LIMIT1000, 10) should be used instead with index-based cursor paging (such as WHEREid>12345) to skip invalid scans. Finally, combining caching, asynchronous aggregation and other means can also further optimize the sorting performance in large data set scenarios.

Aug 04, 2025 am 11:19 AM

sql order by

What is the OFFSET-FETCH clause in SQL for pagination?

OFFSET-FETCHisusedforpaginationinSQL,requiringORDERBYandsupportedinSQLServer,Oracle12c ,andPostgreSQL(notinMySQL).1.OFFSETNROWSskipsNrows.2.FETCHNEXTMROWSONLYretrievesthenextMrows.Itenablesprecisepagecontrolbutslowswithlargeoffsets;keysetpaginationis

Aug 04, 2025 am 11:14 AM

A Complete Guide to SQL: From Basic Syntax to Advanced Query Optimization

SQLmasterybeginswithunderstandingcorecommandsandprogressestoadvancedoptimization.1.Startwithbasicsyntax:useSELECTtoretrievedata,WHEREtofilterrows,INSERTtoaddrecords,UPDATEtomodifydata,DELETEtoremoverecords,ORDERBYtosortresults,andLIMIT/OFFSETforpagin

Aug 04, 2025 am 11:12 AM

sql Query optimization

How do you use a subquery within a SELECT statement in SQL?

AsubqueryintheSELECTclausereturnsasinglevaluetocomputeafieldforeachrow,suchasretrievingadepartmentnameforeachemployeebylookinguprelateddatainanothertable.2.AsubqueryintheWHEREclausefiltersresultsbasedonaconditionderivedfromanotherquery,suchasfindinge

Aug 04, 2025 am 11:08 AM

Implementing SQL Snapshots for Point-in-Time Recovery

SQL snapshots are an efficient means to achieve point-in-time recovery, especially for rapid rollback to a specific point-in-time when misoperation or data is damaged. 1. SQL snapshots are read-only and static database views that record the status of a certain point in time, record data page changes through the sparse file mechanism, which is fast creation speed and low resource utilization. 2. The advantages of using snapshot recovery include fast speed, few resources, no impact on the primary database, and suitable for misoperation of recovery, but cannot replace complete backups. 3. The syntax for creating snapshots is simple, and it is implemented through the RESTORE command when restoring. 4. Practical suggestions include creating before key operations, creating automatically regularly, paying attention to snapshot file growth, and multiple snapshots support multi-point-in-time recovery. 5. Notes include affecting the performance of write operations, snapshot files should be stored and restored separately

Aug 04, 2025 am 11:07 AM

How to export table to CSV in phpMyAdmin

LogintophpMyAdmin,selectthedatabaseandtable.2.Clickthe"Export"tabandchoose"Custom"method.3.SetformattoCSV,enablecolumnheaders,configurefieldseparators(comma),enclosure(quotes),escape(backslash),andlineendings(\n).4.Check"Save

Aug 04, 2025 am 10:22 AM

What is Oracle GoldenGate?

OracleGoldenGateisareal-timedatareplicationandintegrationtoolthatminimizessourcesystemimpactbyusingchangedatacapture(CDC)toreadtransactionlogsandreplicateonlychanges.1.TheExtractprocesscapturesdatachangesfromsourcetransactionlogsintotrailfiles.2.Data

Aug 04, 2025 am 10:15 AM

How do you work with XML data in SQL?

SQLServerprovidesthemostrobustXMLsupportusingmethodslike.value(),.query(),.nodes(),.exist(),and.modify()forqueryingandmodifyingXMLdata;1.StoreXMLinanXML-typedcolumnwithoptionalschemavalidation;2.Extractscalarvalueswith.value()andmultiplenodeswith.nod

Aug 04, 2025 am 09:55 AM

What is the difference between an INNER JOIN and a LEFT JOIN in SQL?

ThemaindifferenceisthatINNERJOINreturnsonlymatchingrowsfrombothtables,whileLEFTJOINreturnsallrowsfromthelefttableandmatchedrowsfromtheright,withNULLsfornon-matches;1.UseINNERJOINtoincludeonlyrecordswithmatchingvaluesinbothtables;2.UseLEFTJOINtoinclud

Aug 04, 2025 am 09:46 AM

Mastering SQL JOIN Operations: A Comprehensive Guide

SQLJOINscombinedatafrommultipletablesusingrelatedcolumns.1.INNERJOINreturnsonlymatchingrows.2.LEFTJOINincludesalllefttablerows,fillingunmatchedwithNULL.3.RIGHTJOINincludesallrighttablerows.4.FULLJOINcombinesallrowsfrombothtables.UseINNERJOINforstrict

Aug 04, 2025 am 09:35 AM

Implementing MySQL Data Version Control with Git

Using Git to implement MySQL data version control can improve collaboration and operation and maintenance efficiency. 1. Why use Git to control MySQL version: Git can record every change, facilitate backtracking and support branch management, and solve problems such as multi-person development conflicts, difficulty in tracing field changes and complex rollbacks. 2. How to incorporate Git management: Export the structure into a readable file and record each change of SQL script, such as using mysqldump to export the structure, write the SQL file and submit it every time. 3. Recommended workflow: Each function corresponds to the branch, change the SQL file to put the /db/migrations/ directory, review the SQL when submitting the PR, and execute the file update structure before going online. 4. Tool recommendations and precautions: Liqu is available

Aug 04, 2025 am 09:29 AM

How do you grant and revoke permissions in SQL?

GRANTandREVOKEstatementsareusedtomanageuserpermissionsinSQL.1.GRANTprovidesprivilegeslikeSELECT,INSERT,UPDATE,DELETE,ALTER,EXECUTE,orALLPRIVILEGESondatabaseobjectstousersorroles.2.SyntaxforgrantingisGRANTprivilege_typeONobject_nameTOuser_or_role,allo

Aug 04, 2025 am 09:19 AM

sql Permissions

What are SQL triggers and how do they work?

TriggersareautomaticallyexecutedinresponsetoINSERT,UPDATE,orDELETEeventsonatableorview.1.TheyruneitherBEFOREorAFTERthetriggeringevent,withBEFOREtriggersusedforvalidationordatamodificationandAFTERtriggersforloggingorupdatingrelateddata.2.Somedatabases

Aug 04, 2025 am 09:14 AM

What are the Best Practices for MySQL Database Security?

Usestrongpasswordswiththevalidate_passwordplugin,applyleastprivilegebygrantingminimalnecessarypermissions,renameorrestrictthedefaultrootaccount,andremoveunusedaccounts.2.BindMySQLtointernalinterfaces,usefirewallstolimitaccesstotrustedIPs,enableSSL/TL

Aug 04, 2025 am 08:37 AM

Database security MySQL Security