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Technical Articles

Database

How to convert a string to uppercase or lowercase in MySQL

ToconvertastringtouppercaseorlowercaseinMySQL,usetheUPPER()andLOWER()functions.1.UseUPPER(str)toconvertastringtouppercase,e.g.,SELECTUPPER('helloworld')returnsHELLOWORLD,orapplyittoacolumnlikeSELECTUPPER(name)FROMusers.2.UseLOWER(str)toconvertastring

Sep 03, 2025 am 07:01 AM

mysql String conversion

What is the OPTIMIZE TABLE command in MySQL?

OPTIMIZETABLEisusedtoreorganizephysicalstorageandreclaimunusedspaceafterlargedeletionsorupdates,particularlyinInnoDBandMyISAMtables;itrebuildsthetablebycopyingonlylivedata,defragmentsstorage,updatesindexstatistics,resetsauto-incrementcountersinsomeca

Sep 03, 2025 am 05:54 AM

How to use the PIVOT operator with dynamic columns in SQL?

To implement dynamic PIVOT operation of unknown column values ??in SQLServer, dynamic SQL must be used. The specific steps are as follows: 1. Recognize that standard PIVOT needs to hardcode column values ??and cannot adapt to dynamically changing categories; 2. Construct dynamic column lists by querying DISTINCT values, and use QUOTENAME() to safely process column names; 3. Splice the generated column names into PIVOT query strings and execute them with EXECsp_executesql; 4. The generated SQL statements can be debugged through PRINT@SQL; this method is suitable for scenarios where column values ??change over time, such as dynamically generating columns by product, month or region, and finally implement flexible and complete dynamic cross-reports, ending with a complete sentence structure.

Sep 03, 2025 am 05:47 AM

How to extract the day from a date in SQL

ToextractthedayfromadateinSQL,useDAY()orEXTRACT(DAYFROM...)dependingonthedatabase:MySQLsupportsbothDAY()andEXTRACT(),PostgreSQLandOracleuseEXTRACT(),SQLServerallowsDAY()orDATEPART(day,...),andSQLiterequiresstrftime('%d',...)whichreturnsazero-paddedst

Sep 03, 2025 am 05:22 AM

sql date

How to set auto increment in phpMyAdmin

TosetautoincrementinphpMyAdmin,whencreatinganewtable,defineacolumn(e.g.,id)withINTtype,enabletheA_Icheckbox,andsetitasPRIMARYKEY.2.Foranexistingtable,gotoStructure,clickChangeonthecolumn,ensureit’sINTtype,checkA_I,setasPrimary,andsave.3.Remember:only

Sep 03, 2025 am 05:20 AM

自動遞增

How to optimize the MySQL server configuration for performance

Setinnodb_buffer_pool_sizeto70–80%ofRAM(e.g.,12Gon16GBRAM)andconfigureinnodb_buffer_pool_instancesto1per1GBofbufferpool(e.g.,8for12G);keepkey_buffer_sizesmall(32–64M)unlessusingMyISAMheavily;increasetmp_table_sizeandmax_heap_table_sizeto256Mifdisk-ba

Sep 03, 2025 am 05:04 AM

performance mysql optimization

How to use Common Table Expressions (CTEs) in MySQL

ACTEisdefinedusingtheWITHclauseandactsasatemporaryresultsetforasinglequery.2.SimpleCTEsimprovereadabilitybyisolatingcalculationslikeaveragesalary.3.MultipleCTEscanbeusedinonequery,separatedbycommas,tobreaklogicintostepssuchascomputingaveragesandranki

Sep 03, 2025 am 04:15 AM

How to import a CSV file into MySQL

Using LOADDATAINFILE is the fastest way to import CSV files into MySQL. 1. Ensure that the CSV file is formatted correctly and placed in MySQL accessible paths or use LOCAL options; 2. Create a table in MySQL that matches the CSV structure; 3. Execute the LOADDATAINFILE command and set the correct separator, quotes and line breaks, and enable local_infile if necessary; 4. If the file is local, use LOADDATALOCALINFILE; in addition, graphical import can be performed through phpMyAdmin. Pay attention to file permissions, field matching, data type, character encoding and other issues to ensure successful import.

Sep 03, 2025 am 04:11 AM

mysql csv

How to Handle Joins in MongoDB

MongoDBhandlesrelationshipsthroughschemadesigninsteadofSQL-stylejoins.Forone-to-few,embedrelateddata;forone-to-manyormany-to-many,usemanualreferenceswith_id.Use$lookupinaggregationfordynamicjoinsbetweencollections,idealforanalytics.Considerdataduplic

Sep 03, 2025 am 04:07 AM

How to create a new user and assign roles in SQL

The method of creating a new user and assigning a role varies from the database management system: in MySQL, use the CREATEUSER command to create a user and grant permissions directly through the GRANT statement or create a role and assign it to the user; in PostgreSQL, CREATEUSER or CREATEROLE is used to create a user, and the permissions are assigned by the database, schema or table through the GRANT statement, and the role can be directly granted to the user; in SQLServer, you must first use CREATELOGIN to create a server-level login name, then use CREATEUSER to create a database user in the database, and finally assign permissions through the system stored procedures or custom roles, such as

Sep 03, 2025 am 02:28 AM

How to handle errors in a stored procedure in SQL

UseTRY...CATCHblockstotraperrorsinstoredprocedures,ensuringthattheCATCHblockrollsbacktransactionsif@@TRANCOUNT>0andre-throwstheerrorusingTHROW.2.CapturedetailederrorinformationwithERROR_NUMBER(),ERROR_MESSAGE(),ERROR_SEVERITY(),ERROR_STATE(),ERROR

Sep 03, 2025 am 02:14 AM

sql stored procedure

How to manage time zones in MySQL?

Use TIMESTAMP data types and configure time zone support to effectively manage time zones in MySQL. Specific practices include: prioritizing TIMESTAMP over DATETIME to achieve automatic time zone conversion, setting the server time zone to UTC to avoid daylight saving time problems, loading the time zone table through mysql_tzinfo_to_sql to support named time zones, setting the session time zone according to user location to automatically adjust the time, using the CONVERT_TZ() function for explicit time zone conversion, and always storing timestamps in the UTC time zone to ensure data consistency, and ultimately ensuring the accuracy of time applications across regions.

Sep 03, 2025 am 02:09 AM

Navicat vs Dbeaver: which is best?

Navicatisbetterforapolished,user-friendlyexperience,whileDBeaverexcelsincustomizationandsupportingawiderangeofdatabases.Navicatoffersasleekinterfaceandrobustfeaturesforeasydatabasemanagement,whereasDBeaver,beingopen-source,providesflexibilityandexten

Sep 03, 2025 am 02:05 AM

How to get the database name you are connected to in SQL?

MySQL:SELECTDATABASE();returnsthecurrentdatabasenameorNULLifnoneisselected.2.PostgreSQL:SELECTcurrent_database();returnsthenameofthecurrentlyconnecteddatabase.3.SQLServer:SELECTDB_NAME();directlyreturnsthecurrentdatabasename.4.Oracle:SELECTnameFROMv$

Sep 03, 2025 am 01:57 AM