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Technical Articles

Database

How to insert an element into a list at a specific position using LINSERT?

The LINSERT command is used to insert new values ??before and after a specific element in the Redis list. Its syntax is: LINSERTkeyBEFORE|AFTERpivotvalue. For example, insert 1.5 after element 1 in the list mylist, use the command LINSERTmylistAFTER11.5; if you want to insert before "middle", use BEFORE and specify the corresponding parameters. Note when using: If pivot does not exist or the key is empty, it will not be inserted and returned -1 or 0; if the key exists but is not a list, an error will be reported; the insertion content can be empty or NULL. To avoid errors, you should first check the key type and current content with TYPE and LRANGE.

Sep 04, 2025 am 09:52 AM

redis LINSERT

How to use the NOW function in MySQL

NOW() returns the current date and time, which is often used to record the exact moments of data operations; 1. It can be used directly in SELECT, such as SELECTNOW() to get the current timestamp; 2. Automatically record the creation time in INSERT, and supports setting DEFAULTNOW() to achieve automatic filling; 3. Automatically update and modify time in UPDATE combined with ONUPDATENOW(); 4. Compared with other functions, NOW() returns the local date and time, CURDATE() returns the date, CURTIME() returns the time, and UTC_TIMESTAMP() returns the UTC time; when using it, make sure that the field type is DATETIME or TIMESTAMP, and it is recommended to

Sep 04, 2025 am 08:51 AM

mysql now function

What are different transaction isolation levels in SQL?

SQLtransactionisolationlevelscontrolhowtransactionsinteractwhenaccessingshareddata,balancingconsistencyandperformancebypreventingdirtyreads,non-repeatablereads,andphantomreads.1.ReadUncommittedallowsdirtyreads,non-repeatablereads,andphantomreads,maki

Sep 04, 2025 am 08:25 AM

sql transaction isolation level

How to use the INSERT IGNORE statement in MySQL?

INSERTIGNOREinMySQLallowsinsertingrowswhilesilentlyskippingerrorslikeduplicatekeysorinvaliddata,makingitidealforensuringrecordsexistwithoutduplicates.1)Useitwhenyouwanttoinsertarowonlyifitdoesn’talreadyexistbasedonuniqueorprimarykeyconstraints.2)Itpr

Sep 04, 2025 am 08:23 AM

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