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Technical Articles

Database

Mysql Tutorial

What is the purpose of the LOCK TABLES statement in MySQL?

LOCKTABLESpreventsdatainconsistenciesinnon-transactionalengineslikeMyISAMbyserializingaccess;2.ItallowscontroloverconcurrencyusingREADlocks(shared,forreadingonly)andWRITElocks(exclusive,fortheholderonly);3.Itensuresatomicityacrossmultipletablesbylock

Aug 16, 2025 am 12:36 AM

How to use the GROUP BY clause in MySQL?

TheGROUPBYclauseinMySQLisusedtogrouprowswithidenticalvaluesinspecifiedcolumns,enablingsummarycalculationswithaggregatefunctionslikeCOUNT(),SUM(),AVG(),MAX(),andMIN();forexample,"SELECTregion,COUNT()AStotal_salesFROMsalesGROUPBYregion"groups

Aug 16, 2025 am 12:05 AM

mysql group by

How to handle emoji characters in MySQL

To correctly handle emoji characters in MySQL, you must use the utf8mb4 character set. 1. Make sure that the database, table and column use utf8mb4 and utf8mb4_unicode_ci; 2. Set the client and server character set to utf8mb4 in the MySQL configuration file, and enable innodb_large_prefix; 3. Specify the charset to utf8mb4 when applying the connection; 4. Verify the configuration through SHOWVARIABLES and SHOWCREATETABLE; 5. Pay attention to the utf8mb4 index length limit and limit the index column length to within 191 characters. Only use utf8m in the entire data link

Aug 15, 2025 am 11:14 AM

What is the difference between MyISAM and InnoDB in MySQL?

InnoDB supports transaction and ACID features, but MyISAM does not support it; 2. InnoDB uses row-level locks to improve concurrency performance, while MyISAM uses table-level locks to easily cause blockage; 3. InnoDB supports foreign key constraints to ensure data integrity, but MyISAM does not support it; 4. InnoDB has crash recovery capabilities, and MyISAM is prone to table damage; 5. MyISAM may be faster in pure read scenarios, but InnoDB performs better under mixed loads; 6. Since MySQL5.6, InnoDB has supported full-text indexing and no longer lag behind; 7. InnoDB optimizes data access through buffer pools, and MyISAM only caches indexes. In summary, InnoDB is suitable for most modern applications, and My

Aug 15, 2025 am 11:06 AM

How to import a database using mysqldump

mysqldumpisusedtoexport,notimport,adatabase;toimport,usethemysqlcommand-lineclient.1.Ensureyouhavea.sqldumpfilecreatedviamysqldump.2.Createthetargetdatabaseifitdoesn’texistusingCREATEDATABASE.3.ImporttheSQLfilewithmysql-uusername-pdatabase_name

Aug 15, 2025 am 10:56 AM

Database import

What is a full-text search in MySQL?

Full-textsearchinMySQLenablesefficient,relevance-rankedtextsearchingincharacter-basedcolumnsusingFULLTEXTindexesandMATCH()...AGAINST()syntax,supportingnaturallanguage,boolean,andqueryexpansionmodesprimarilyonInnoDBandMyISAMengines,makingitidealforlar

Aug 15, 2025 am 10:43 AM

mysql research all

How to implement full-text search in MySQL

Create a FULLTEXT index to enable full-text search, which can be added when creating a table or using ALTERTABLE; 2. Use MATCH()...AGAINST() syntax to perform searches, support natural language mode, Boolean mode and query extensions; 3. Pay attention to restrictions and best practices such as minimum word length, stop words, differences between InnoDB and MyISAM; 4. By combining WHERE conditions, using EXPLAIN to analyze and reasonably maintain index optimization performance, MySQL full-text search can meet the needs of most application scenarios.

Aug 15, 2025 am 09:27 AM

mysql research all

How to optimize a MySQL query?

Use appropriate indexes to create indexes for columns involved in WHERE, JOIN, ORDERBY and GROUPBY, give priority to compound indexes but avoid over-index, and verify index usage through EXPLAIN; 2. Write efficient queries, avoid SELECT*, do not use functions on index columns, use LIMIT reasonably, handle OR conditions carefully, and give priority to EXISTS rather than IN subqueries; 3. Optimize JOIN and table structure, ensure that the join columns are indexed, select the correct JOIN type, de-normalize appropriately to reduce JOIN, and use smaller data types to improve efficiency; 4. Use EXPLAIN and EXPLAINFORMAT=JSON to analyze query execution plans,

Aug 15, 2025 am 09:02 AM

How to use transactions in MySQL

To use MySQL transactions correctly, it is necessary to ensure that the transaction is started explicitly through STARTTRANSACTION or BEGIN, and relevant SQL operations are performed. If all operations are successful, COMMIT commit, if there is an error, ROLLBACK rollback. You can use SAVEPOINT to set a save point to achieve partial rollback. In the application, you need to manage exceptions in combination with the try-catch mechanism. At the same time, pay attention to turning off the autocommit mode to avoid automatic commit, keep the transaction short to improve performance, and select the appropriate isolation level according to business needs to ensure data consistency and integrity.

Aug 15, 2025 am 08:31 AM

How to use the mysql command-line client effectively

Use~/.my.cnfwithchmod600tosecurelysavecredentialsandenablepasswordlesslogin;2.Enableauto-rehashinconfigorcommandlinefortabcompletionofdatabases,tables,andcolumns;3.Insidetheclient,use\utoswitchdatabases,\Gforverticaloutput,\sforstatus,\ptoprintbuffer

Aug 15, 2025 am 07:08 AM

How to lock tables in MySQL

The table can be locked manually using LOCKTABLES. The READ lock allows multiple sessions to read but cannot be written. The WRITE lock provides exclusive read and write permissions for the current session and other sessions cannot read and write. 2. The lock is only for the current connection. Execution of STARTTRANSACTION and other commands will implicitly release the lock. After locking, it can only access the locked table; 3. Only use it in specific scenarios such as MyISAM table maintenance and data backup. InnoDB should give priority to using transaction and row-level locks such as SELECT...FORUPDATE to avoid performance problems; 4. After the operation is completed, UNLOCKTABLES must be explicitly released, otherwise resource blockage may occur.

Aug 15, 2025 am 04:04 AM

mysql lock table

How to create a copy of a table in MySQL?

Tocopyonlythetablestructurewithindexesandconstraints,useCREATETABLEnew_tableLIKEoriginal_table;thiscreatesanemptytablewiththesameschema,includingprimarykeysandauto-incrementsettingsbutwithoutdata.2.Tocopybothstructureanddata,useCREATETABLEnew_tableAS

Aug 15, 2025 am 03:58 AM

mysql 復(fù)制表

How to use the WHERE clause in MySQL?

TheWHEREclauseinMySQLisusedtofilterrecordsbasedonspecifiedconditions,allowingprecisedataretrieval,modification,ordeletion;itworkswithSELECT,UPDATE,andDELETEstatementsbyapplyingconditionsusingcomparisonoperatorslike=,,,=,logicaloperatorsAND,OR,NOT,and

Aug 15, 2025 am 03:56 AM

mysql

How to use the EXISTS operator in MySQL

EXISTS is used to check whether the subquery returns rows. The answer is: 1. EXISTS judges the existence of data through subquery in the WHERE clause, and returns TRUE or FALSE; 2. The basic syntax is SELECT column name FROM table 1WHEREEXISTS (SELECT1FROM table 2WHERE condition). The subquery is executed once per row, and uses SELECT1 placeholder and short-circuit evaluation; 3. In the example, the customer with an order is found through EXISTS, that is, SELECTnameFROMcustomerscWHEREEXISTS(SELECT1FROMordersoWHEREo.customer_id=c.cust

Aug 15, 2025 am 03:04 AM

mysql