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Technical Articles

Database

Mysql Tutorial

How to use the CURTIME function in MySQL

CURTIME()returnsthecurrenttimeinHH:MM:SSformatwithoutthedate;1.UseSELECTCURTIME()togetthecurrentsystemtime;2.IncludeaprecisionargumentlikeCURTIME(3)forfractionalsecondsuptomicroseconds;3.InsertCURTIME()intoTIMEtypecolumnstorecordstarttimes;4.Useitinf

Sep 04, 2025 am 06:51 AM

How to handle NULL values in MySQL?

UseISNULLorISNOTNULLtocheckforNULLvaluesbecausestandardcomparisonswith=or!=returnunknown;2.ApplyCOALESCE()orIFNULL()toreplaceNULLswithdefaultvaluesinresults;3.WrapnullablecolumnsinfunctionslikeCOALESCE()duringarithmetictopreventNULLoutcomes;4.Enforce

Sep 04, 2025 am 06:47 AM

mysql null value

How to create a user in MySQL

Create a MySQL user first, first use the administrator account to log in, execute CREATEUSER to specify the user name, host and password, then give the corresponding permissions through the GRANT statement, and finally run FLUSHPRIVILEGES to take effect, 1. Connect to MySQL: mysql-uroot-p; 2. Create a user: CREATEUSER'username'@'host'IDENTIFIEDBY'password'; 3. Grant permissions: GRANTprivilege_typeONdatabase_name.table_nameTO'username'@'host'; 4. Refresh permissions: FLU

Sep 04, 2025 am 02:42 AM

How to select a database in MySQL

UsetheUSEdatabase_name;commandtoselectadatabaseinMySQL,replacingdatabase_namewiththedesireddatabase.2.ListavailabledatabaseswithSHOWDATABASES;ifunsurewhichonesexist.3.VerifythecurrentlyselecteddatabaseusingSELECTDATABASE();whichreturnstheactivedataba

Sep 04, 2025 am 12:06 AM

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 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 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

How to insert if not exists in MySQL (UPSERT)

UseINSERTIGNOREtoinsertarowonlyifitdoesn'texist,silentlyskippingduplicatesbasedonauniqueconstraint;2.UseINSERT...ONDUPLICATEKEYUPDATEtoupsert,insertingifnotexistsorupdatingifitdoes;3.AvoidREPLACEINTOasitdeletesandreinserts,potentiallycausingdatalosso

Sep 03, 2025 am 12:47 AM

mysql Upsert

How to perform a boolean full-text search in MySQL

To perform Boolean full text search, you must first create a FULLTEXT index, and then use MATCH()...AGAINST() with INBOOLEANMODE and Boolean operators; 1. Make sure that FULLTEXT index has been created for the search column, which can be implemented through ALTERTABLE or CREATETABLE; 2. Use MATCH()...AGAINST('searchterms'INBOOLEANMODE) syntax to perform searches; 3. Use (must include), - (must exclude), "(exact phrase), * (prefix wildcard), () (group), ~ (optional downright) and other operators to accurately control the results; 4

Sep 03, 2025 am 12:26 AM

How to get the current date and time in MySQL?

To get the current date and time, you should use the NOW() function because it returns the date and time when the statement starts to execute; if it needs to be precise to the time of the function execution moment, use SYSDATE(); use CURDATE() when only the date is needed, and use CURTIME() when only the time is needed; these functions can be used to query, insert or set default values, such as CREATETABLElogs(idINTPRIMARYKEY, messageTEXT, created_atDATETIMEDEFAULTNOW());, NOW() is usually recommended unless the real-time feature of SYSDATE() is required.

Sep 02, 2025 am 08:27 AM

How to find all leaf nodes in a tree structure in MySQL

Inanadjacencylistmodel,leafnodesarefoundusingaLEFTJOINtoidentifynodeswithoutchildren:SELECTt1.id,t1.nameFROMtreet1LEFTJOINtreet2ONt1.id=t2.parent_idWHEREt2.parent_idISNULL;2.Inanestedsetmodel,leafnodesareidentifiedwherergt=lft 1:SELECTid,nameFROMtree

Sep 02, 2025 am 07:51 AM