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Technical Articles

Database

How to edit data in phpMyAdmin

ToeditdatainphpMyAdmin,loginandselectthedatabaseandtablefromthesidebar.2.Clickthepenciliconnexttothedesiredrow,modifythefieldvalueswhilerespectingdatatypes,andclickGotosave.3.Forbulkedits,usetheSQLtabwithanUPDATEstatement,ensuringaproperWHEREclauseto

Aug 04, 2025 pm 04:16 PM

What is the role of the information_schema database in MySQL?

Theinformation_schemaisaread-onlysystemdatabaseinMySQLthatprovidesmetadataaboutallotherdatabasesandobjects.1.Itservesasacentralsourceofmetadata,containingdetailsaboutdatabases,tables,columns,indexes,views,routines,triggers,anduserprivileges;forexampl

Aug 04, 2025 pm 03:47 PM

mysql 信息模式

Leveraging MySQL CHECK Constraints in MySQL 8.0

The CHECK constraint in MySQL8.0 does not really work because it parses but ignores the constraint; 1. It retains CHECK for compatibility and future extensions; 2. CHECK can be used as a document description; 3. Alternative methods include using triggers, application layer verification and stored procedures; 4. When using it, be careful not to rely on it for data verification. Multiple CHECK constraints are invalid, and migration scripts require additional processing, and some tools may prompt that they do not support it.

Aug 04, 2025 pm 03:35 PM

How to handle cascading deletes and updates with foreign keys in MySQL?

CascadingdeletesandupdatesinMySQLautomaticallymaintainreferentialintegritybypropagatingchangesfromparenttochildtables.2.UseONDELETECASCADEtoautomaticallydeletechildrecordswhenaparentrecordisdeleted,andONUPDATECASCADEtoupdatecorrespondingforeignkeyval

Aug 04, 2025 pm 03:33 PM

How to format dates in MySQL using DATE_FORMAT?

Date formatting in MySQL is implemented by the DATE_FORMAT() function, which converts datetime values into strings of the specified format. 1. The basic syntax is DATE_FORMAT(date,format), where date is a valid date expression and format is a string containing a format starting with %. 2. Common format characters include: %Y (four-digit year), %m (two-digit month), %d (two-digit day), %H (24-hour hours), %i (minutes), %p (AM/PM), etc. 3. Sample application: Use '%M%d,%Y' to output "January05,2025", '%m/%d/%Y' to generate the beauty of "01/05/2025"

Aug 04, 2025 pm 03:01 PM

SQL Server Distributed Transactions

A distributed transaction is a set of operations performed between multiple databases or servers, ensuring that all operations are either successful or fail. Its core is to ensure cross-system data consistency and rely on MSDTC service coordination. The steps to enable: 1. Ensure the server accesses MSDTC; 2. Open the firewall port; 3. Set up the linked server to enable distributed transactions; 4. Use the BEGINDISTRIBUTEDTRANSACTION command. Common problems include timeout deadlock, DTC configuration errors, and performance degradation. Solutions include reducing transaction operations, checking network configuration, and avoiding unnecessary queries and connection pool interference. Whether to use it depends on the scene. High consistency across systems is suitable for use. Otherwise, local transactions or asynchronous operations are recommended.

Aug 04, 2025 pm 02:59 PM

What is a FULL OUTER JOIN in SQL and how does it differ from other joins?

AFULLOUTERJOINreturnsallrowsfrombothtables,includingmatchedandunmatchedrecords,withNULLswherenomatchexists.1.ItcombinesmatchingrowslikeanINNERJOIN.2.ItincludesunmatchedrowsfromthelefttablewithNULLsforrighttablecolumns.3.Itincludesunmatchedrowsfromthe

Aug 04, 2025 pm 02:58 PM

Database Statistics and Their Impact on SQL Query Plans

The accuracy of database statistics directly affects the optimization effect of SQL query plan. Statistics are metadata about the distribution of tables and index data, including the number of rows, the number of different values, data distribution and index selectivity, etc., for the optimizer to estimate the cost of execution paths and select the optimal plan. Inaccurate statistical information will lead to problems such as misselecting the full table scan, unused indexes, improper parallel planning, and unreasonable association order. Maintenance methods include: 1. Regular update of statistical information; 2. Pay attention to high-frequency query columns; 3. Avoid over-update; 4. Use sampling to reduce overhead; 5. Pay attention to partition table configuration. Determining whether it is a statistical information problem can be achieved by checking the changes in the execution plan, index usage, result set estimation deviation and recent data changes. Mastering statistical information maintenance strategies can show

Aug 04, 2025 pm 02:45 PM

數(shù)據(jù)庫統(tǒng)計 SQL查詢計劃

What are the limitations of MySQL VIEWs?

MySQLviewshaveseverallimitationsthataffectperformanceandfunctionality:1.Theyincurperformanceoverheadbecausetheyarevirtualandre-executethebasequeryeachtime,leadingtoslowresponsesoncomplexjoinsorlargedatasets;2.Theyarenotalwaysupdatable,asMySQLrestrict

Aug 04, 2025 pm 02:28 PM

視圖限制

Oracle vs SQL Server performance comparison

Oraclegenerallyperformsbetterinlarge-scale,high-concurrencyenvironmentsduetoadvancedscalabilityfeatureslikeRACandsuperiorhandlingofcomplexworkloads,whileSQLServerexcelsinWindowsandAzureecosystemswitheasieradministrationandstrongOLTPperformance;1.Fore

Aug 04, 2025 pm 02:21 PM

How to manage max_allowed_packet size in MySQL?

To manage the max_allowed_packet size of MySQL, first check the current value using SHOWVARIABLESLIKE'max_allowed_packet';, then you can temporarily set SETGLOBALmax_allowed_packet=1073741824; (1GB) as needed, or permanently modify the configuration file such as /etc/mysql/mysql.conf.d/mysqld.cnf to add max_allowed_packet=1G, and set it in the [mysql] and [mysqldump] paragraphs to ensure both client tools and

Aug 04, 2025 pm 02:18 PM

How can you use common table expressions (CTEs) to make complex SQL queries more readable?

CommonTableExpressions(CTEs)improveSQLqueryreadabilityandmaintainabilitybybreakingcomplexlogicintonamed,reusablesteps.1.Theybreakdowncomplexqueriesintologicalsteps,replacingdeeplynestedsubquerieswithclear,sequentialblocks—makingthedatatransformationp

Aug 04, 2025 pm 02:02 PM

sql CTE

How to Use Indexes to Speed Up MySQL Queries?

IndexesimproveMySQLqueryperformancebyenablingfastrowlookupwithoutfulltablescans.2.UseB-Tree,hash,full-text,orcompositeindexesbasedonqueryneeds.3.IdentifyslowquerieswiththeslowquerylogandEXPLAIN.4.CreateindexesoncolumnsinWHERE,JOIN,ORDERBY,andGROUPBYc

Aug 04, 2025 pm 01:47 PM

Advanced MySQL Security Hardening Techniques

The core methods of MySQL security reinforcement include: 1. Restrict user permissions, minimize authorization, create a dedicated account and regularly review permissions; 2. Strengthen identity authentication, enable strong password policies, limit the number of login failures and use SSL connections; 3. Lock server access, bind intranet IP, configure firewall and disable remote root login; 4. Turn on auditing and logging, and regularly check log files to facilitate tracking suspicious behavior. These measures can effectively improve database security and prevent security risks caused by improper default configuration.

Aug 04, 2025 pm 01:30 PM