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Technical Articles

Database

What is the role of the database administrator in MySQL?

ADBAsetsupandconfiguresMySQLinstanceswithoptimalversions,storageengines,andconfigurationparameterstopreventperformanceissues.2.Theymanageuseraccessandsecuritybycreatingaccounts,assigningprivileges,enforcingpasswordpolicies,andmonitoringforunauthorize

Sep 05, 2025 am 04:12 AM

mysql 數據庫管理員

How to get the length of a list using LLEN?

LLEN is a command used in Redis to obtain the length of the list. Its time complexity is O(1). It is called through the LLENkey_name syntax when used. When the key does not exist, it returns 0. If the key type is not List, an error will be reported. Common uses include stating message queues, limiting queue length, etc.; queue management can be implemented in combination with LPUSH, RPUSH, LTRIM and other commands.

Sep 05, 2025 am 04:00 AM

How to set primary key in phpMyAdmin

TosetaprimarykeyinphpMyAdmin,usethe"Primary"checkboxwhencreatinganewtableorselectthecolumnandchoose"Primary"fromthe"Withselected"dropdownforexistingtables;1.Whencreatinganewtable,definethecolumn,check"Primary",

Sep 05, 2025 am 02:52 AM

primary key

Benchmarking MySQL Performance: Tools and Methodologies

The key to MySQL performance benchmarking is to select the right tools and methods and develop scientific testing plans. 1. Common tools include sysbench (suitable for OLTP stress testing), mysqlslap (lightweight official tool), HammerDB (graphical enterprise-level testing) and JMeter (flexible database stress testing); 2. The test plan needs to clarify the goals, set parameters, use real data, and control variables to ensure accuracy; 3. Pay attention to core indicators such as QPS/TPS, response time, resource usage, and error rate; 4. The test environment should be close to production, maintain hardware consistency, network stability, shut down interfering services, multiple runs to average, and avoid direct testing in the production environment.

Sep 05, 2025 am 02:27 AM

How to use transaction control in Navicat?

Using transaction control in Navicat ensures that multiple SQL operations are either successful or all fail. 1. Ensure that the database supports transactions (such as MySQL's InnoDB engine); 2. Turn off the automatic commit mode (execute SETautocommit=0); 3. Enter STARTTRANSACTION or BEGIN in the query window to enable transactions; 4. Execute multiple SQL statements; 5. Select COMMIT commit or ROLLBACK rollback based on the execution results; 6. Use the query history function to assist in debugging and retry; 7. Pay attention to avoid connection interruptions and long-term failure to commit transactions; 8. It is recommended to operate in the test environment and back up data in advance.

Sep 05, 2025 am 02:26 AM

How to use RANK() and DENSE_RANK() in MySQL

MySQL supports RANK() and DENSE_RANK() window functions since version 8.0, but was not supported in the previous version. 1. RANK() gives the same ranking when the values ??are equal, but subsequent rankings create gaps; 2. DENSE_RANK() ranks the same when the values ??are equal and there is no gaps in the future; 3. You can sort by group through PARTITIONBY; for versions below MySQL8.0, variable simulation is required. It is recommended to upgrade to obtain complete support. Use SELECTVERSION() to check the version to ensure that the window function function is correctly applied.

Sep 05, 2025 am 01:41 AM

How to convert a string to uppercase in SQL

ToconvertastringtouppercaseinSQL,usetheUPPER()function,whichiswidelysupportedacrossdatabaseslikeMySQL,PostgreSQL,SQLServer,Oracle,andSQLite;forexample,SELECTUPPER('helloworld')returns'HELLOWORLD',applyingUPPER()toacolumnlikeSELECTUPPER(name)FROMusers

Sep 05, 2025 am 01:40 AM

How to get the number of members in a Set using SCARD?

To find out the number of elements of a collection in Redis, use the SCARD command. 1.SCARD (SetCardinality) returns the number of set members of the specified key, with a time complexity of O(1), which is efficient and fast; 2. If the key does not exist, return 0, which is suitable for checking empty sets or tracking the number of unique values; 3. Commonly used for user analysis, cache systems, speed limit scenarios, etc.; 4. Compared with SMEMBERS, it is better to perform, and suitable for only counting rather than obtaining all members; 5. When using it, make sure that the key is set type and pay attention to the difference from other data structures.

Sep 05, 2025 am 01:14 AM

What is the SQL syntax for an INSERT INTO SELECT statement?

ToinsertdatausingaSELECTqueryinSQL,usetheINSERTINTOSELECTsyntax.1.Ensurecolumncountanddatatypesmatchbetweenthesourceandtargettables.2.Optionallylistcolumnsexplicitlyforsafetyoruse*ifstructuresalign.3.ApplyaWHEREclausetofilterrowsasneeded.4.Tocreatean

Sep 05, 2025 am 01:03 AM

sql

How to use a subquery in the FROM clause in SQL

AsubqueryintheFROMclause,alsoknownasaderivedtableorinlineview,isusedtocreateatemporaryresultsetthatcanbetreatedlikearegulartableintheouterquery,anditmustbeenclosedinparenthesesandassignedanaliastoreferenceitscolumns,suchasinthebasicsyntax:SELECTcolum

Sep 05, 2025 am 12:45 AM

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