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Technical Articles

Database

What is the purpose of the ON DUPLICATE KEY UPDATE statement in MySQL?

TheONDUPLICATEKEYUPDATEstatementinMySQLallowsanINSERToperationtoupdateanexistingrowifaduplicateuniqueorprimarykeyisfound,avoidingerrorsandenablingefficientupserts;whenaduplicateisdetected,thespecifiedcolumnsareupdatedusingtheVALUES()functiontoreferen

Sep 04, 2025 am 08:21 AM

Redis vs databases: can I use transactions?

Using Redis for transactions is complex compared to traditional databases. Traditional databases such as MySQL or PostgreSQL provide full ACID features, while Redis provides limited atomic execution through MULTI/EXEC commands. Transactions in traditional databases ensure data consistency and integrity, while transactions in Redis focus more on speed, sacrificing some consistency guarantees. When choosing, you need to decide based on application needs: when strong ACID guarantee is required, select traditional databases; when pursuing high performance and tolerating certain inconsistencies, Redis may be more suitable.

Sep 04, 2025 am 08:11 AM

How to find the position of a character in a string in SQL

TofindthepositionofacharacterorsubstringinastringinSQL,usePOSITION()inPostgreSQL,CHARINDEX()inSQLServer,INSTR()inMySQLandOracle,orLOCATE()inMySQL,allofwhichreturnthe1-basedindexofthefirstoccurrenceand0ifnotfound,withsyntaxandoptionalparametersvarying

Sep 04, 2025 am 08:05 AM

How to use the EXCEPT operator in SQL

TheEXCEPToperatorinSQLreturnsrowsfromthefirstquerythatarenotpresentinthesecondquery,requiringbothqueriestohavethesamenumberofcolumnswithcompatibledatatypes,anditautomaticallyremovesduplicateswhiletreatingNULLsasequal;itissupportedinPostgreSQL,SQLServ

Sep 04, 2025 am 07:42 AM

sql except

What is the purpose of the DISTINCT keyword in MySQL?

TheDISTINCTkeywordinMySQLremovesduplicaterowsfromqueryresults,returningonlyuniquevaluesbasedontheselectedcolumns;itworksbytreatingrowsasduplicatesonlyifallselectedcolumnvaluesareidentical,includingNULLsasequal,andisappliedtosinglecolumnstoeliminatere

Sep 04, 2025 am 07:15 AM

How to use transactions in SQL

ASQLtransactionisasinglelogicalunitofworkthatensuresdataintegritybyfollowingACIDprinciples:atomicity,consistency,isolation,anddurability;2.TransactionsarecontrolledusingBEGIN(orSTARTTRANSACTION),COMMITtosavechanges,andROLLBACKtoundothem;3.Example:Tra

Sep 04, 2025 am 07:09 AM

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 Implement Data Masking in MongoDB

DatamaskinginMongoDBisachievedthroughapplication-leveltransformations,aggregationpipelines,andsyntheticdatagenerationtoprotectsensitiveinformation.First,distinguishmaskingfromencryption:maskingirreversiblyreplacessensitivedatawithrealisticfakevalues,

Sep 04, 2025 am 06:38 AM

mongodb 數(shù)據(jù)掩碼

How to select rows where a column contains only numbers in SQL?

To filter rows that contain only numbers, you need to select methods according to the database type: 1.MySQL uses WHEREyour_columnREGEXP'^[0-9] $'; 2.PostgreSQL uses WHEREyour_column~'^[0-9] $'; 3.SQLServer uses WHEREyour_columnNOTLIKE'%1%'ANDyour_columnISNOTNULLANDyour_column''; 4.SQLite recommends enabling regularity or external logic processing; these methods ensure that the column value only contains numeric characters and excludes null values, which are suitable for pure numeric string filtering. 0-

Sep 04, 2025 am 04:45 AM

How to use the AVG function in SQL

TheAVGfunctioninSQLcalculatestheaverageofanumericcolumnbysummingnon-NULLvaluesanddividingbytheircount,asshowninSELECTAVG(column_name)FROMtable_name;itignoresNULLsbydefault,canbegroupedwithGROUPBYtocomputeaveragespercategory,filteredwithHAVINGwhenused

Sep 04, 2025 am 04:26 AM

How to Secure Your MongoDB Database

Enabling authentication, restricting network access, enabling encryption and keeping updates are the core measures to protect MongoDB. First, enable authentication and use a strong password to create a user with minimal permission; secondly, restrict access through bindIp and firewall to avoid exposure to the public network; then enable TLS/SSL encryption to transmit data, and encrypt data at rest in combination with file system or MongoDB native functions; finally update the version regularly, enable audit logs and monitor abnormal behaviors to ensure database security.

Sep 04, 2025 am 04:10 AM

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 get the last day of the month in SQL?

SQLServer uses the EOMONTH() function; 2.MySQL and Oracle use the LAST_DAY() function; 3.PostgreSQL is calculated by DATE_TRUNC plus interval; 4.SQLite uses the date function to combine string instructions; select the corresponding method according to different databases to accurately obtain the last day of the month.

Sep 04, 2025 am 02:27 AM