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Technical Articles

Database

How do you create and manage views in a SQL database?

AviewinSQLisavirtualtablebasedonasavedSELECTquerythatsimplifiesdataaccessandenhancessecurity.1.Tocreateaview,useCREATEVIEWwithaSELECTstatementtodefineitsstructure.2.Tomodifyaview,useCREATEORREPLACEVIEWorALTERVIEWdependingonthedatabasesystem.3.Todelet

Aug 05, 2025 pm 05:36 PM

Database management SQL視圖

What is the EXCEPT (or MINUS) operator in SQL and how does it work?

EXCEPTreturnsrowsfromthefirstquerynotpresentinthesecond,requiringmatchingcolumncountandcompatibledatatypes,withduplicatesremovedandresultcolumnnamesfromthefirstquery;1.Ordermatters:AEXCEPTB≠BEXCEPTA;2.Duplicatesareautomaticallyremoved;3.OracleusesMIN

Aug 05, 2025 pm 05:33 PM

What are synonyms in SQL and what are they used for?

SynonymsinSQLarealternativenamesfordatabaseobjectsthatsimplifyaccess,improveschemaindependence,providelocationtransparency,andenhancesecuritythroughabstraction.1.Theysimplifyobjectaccessbyallowingshorterormoreconvenientnamesforcomplexorfullyqualified

Aug 05, 2025 pm 05:17 PM

How to unpivot data in MySQL (columns to rows)?

MySQL does not have a built-in UNPIVOT operator, but column conversion can be achieved by combining SELECT and UNIONALL. 1. Write a separate SELECT statement for each column, convert the column value into rows, and add an identification column (such as quarter); 2. Use UNIONALL to merge all results to ensure that the output structure of each query is consistent; 3. If there are multiple groups of indicators (such as sales, cost), you can expand the SELECT statement and add the indicator type column; 4. Finally sort it as needed. Although this method does not support dynamic columns and is verbose, it has strong compatibility, is suitable for all MySQL versions, and has reliable performance.

Aug 05, 2025 pm 05:13 PM

mysql 數(shù)據(jù)透視

Optimizing MySQL for High-Volume Transaction Processing

Tohandlehigh-volumetransactionsinMySQL,useInnoDBasthestorageengine,tuneitssettingslikebufferpoolsizeandlogfilesize,optimizequerieswithproperindexing,andmanageconnectionsefficiently.First,switchtoInnoDBforrow-levellockingandACIDcomplianceusingALTERTAB

Aug 05, 2025 pm 04:30 PM

How do you create and execute a stored procedure in SQL?

Create stored procedures using CREATEPROCEDURE statement to define names, parameters and SQL code blocks; 2. In MySQL, DELIMITER needs to change the separator to include the BEGIN...END structure; 3. The input and output functions can be implemented through IN, OUT or INOUT parameters; 4. Use CALL (MySQL) or EXEC (SQLServer) to execute stored procedures; 5. Use DROPPROCEDUREIFEXISTS to check and delete existing procedures to avoid errors; 6. The process can be modified or recreated through ALTERPROCEDURE; 7. Stored procedures can be encapsulated, reusable logic, improve performance, and centrally manage database operations, and execute

Aug 05, 2025 pm 04:21 PM

sql stored procedure

Optimizing MySQL for E-commerce Product Search

TooptimizeproductsearchinMySQL,usetherightindexingstrategybyaddingindexesonsearchablecolumnslikeproduct_name,category_id,brand_id,orprice,andconsidercompositeindexesformultiplefilters.Avoidover-indexingtopreventwriteoverhead.Structurequeriesefficient

Aug 05, 2025 pm 03:48 PM

How to Set up a Master-Master Replication in MySQL?

Master-MasterreplicationinMySQLcanbeconfiguredbyfollowingthesesteps:1.EnsuretwoMySQLserversarenetwork-accessible,useuniqueserver-ids,enablebinarylogging,synchronizetimeviaNTP,andallowport3306throughthefirewall;2.Configureeachserver’smy.cnfwithuniques

Aug 05, 2025 pm 03:29 PM

What is the MySQL thread cache and how does it work?

TheMySQLthreadcachereducesthreadcreationoverheadbyreusingthreadsfromdisconnectedclients;1.Itstoresidlethreadsinsteadofdestroyingthem,allowingreusefornewconnections;2.Itismosteffectiveinhigh-connection-churnenvironmentslikewebapplicationswithshort-liv

Aug 05, 2025 pm 03:19 PM

How to Use the LIMIT Clause for Pagination in MySQL?

When using LIMIT for MySQL paging, you must combine ORDERBY and pay attention to performance issues; the specific steps are: 1. Use SELECTFROMtable_nameLIMIToffset, row_count to implement paging; 2. Calculate offset by (page_number-1)page_size; 3. Always add ORDERBY to ensure the consistent results; 4. Consider using cursor-based paging for large offsets to improve performance; 5. Ensure that the columns of ORDERBY have been indexed to speed up querying.

Aug 05, 2025 pm 03:11 PM

What are materialized views in SQL and how do they differ from standard views?

Materializedviewsstoreprecomputedqueryresultsondiskforfasteraccess,unlikestandardviewsthatexecutequeriesondemand.1)Theyimproveperformanceforcomplexqueriesandrepetitivereadsbyphysicallysavingdata.2)Theyrequireperiodicrefreshingtostaycurrent,supporting

Aug 05, 2025 pm 02:55 PM

sql Materialized view

How to use the ON DUPLICATE KEY UPDATE statement in MySQL?

ONDUPLICATEKEYUPDATE is used to handle unique key or primary key conflicts. 1. When there is duplication of insertion data, no error is reported but the specified field is updated; 2. Applicable to counters, data synchronization and other scenarios; 3. The syntax is INSERTINTO...VALUES...ONDUPLICATEKEYUPDATEcolumn=VALUES(column); 4. VALUES(column) obtains the value inserted in the original plan; 5. Only trigger updates when a unique key conflict occurs; 6. Each duplicate record is processed independently; 7. Pay attention to unexpected updates of AUTO_INCREMENT and TIMESTAMP columns; 8. It can avoid complex logic of checking first and then inserting.

Aug 05, 2025 pm 02:34 PM

What is an Oracle SID?

TheOracleSIDuniquelyidentifiesadatabaseinstanceonasystem;1)Itdistinguishesinstancesbyassociatingthemwithspecificprocessesandmemoryareas;2)ItisusedbytheOS,OracleNet,andadministrativetoolstotargetthecorrectinstance;3)Unliketheservicename,whichrepresent

Aug 05, 2025 pm 02:14 PM

What is a correlated subquery in MySQL and what are its performance implications?

AcorrelatedsubqueryinMySQLdependsontheouterqueryandexecutesonceperouterrow,asshowninaquerycomparingeachemployee'ssalarytotheirdepartment'saverage;1.Itworksbyreferencingoutercolumns(e.g.,e1.department)andrecalculatingforeachrow;2.Itcanbeslowduetorepea

Aug 05, 2025 pm 01:57 PM