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Technical Articles

Database

Mysql Tutorial

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

How to find tables without a primary key in MySQL

TofindtableswithoutaprimarykeyinMySQL,useaqueryoninformation_schema;first,excludesystemdatabasesandviews,thenidentifytablesnothavingaprimarykeyconstraintviaKEY_COLUMN_USAGEorTABLE_CONSTRAINTS;1.RuntheprovidedSELECTqueryfilteringoutsystemschemasandeng

Aug 15, 2025 am 02:56 AM

mysql full text search

MySQL full-text search is suitable for keyword search of text content. Before use, you need to create a FULLTEXT index; full-text search supports natural language and Boolean pattern query, and improves efficiency by inverting indexes; common misunderstandings include direct query without indexes, keyword length limitations and stop word problems; you can improve accuracy by modifying ft_min_word_len, custom stop words or using Boolean pattern; applicable scenarios are non-precise matching requirements such as blogs and news, which are not suitable for code log retrieval or high concurrency real-time search; pay attention to problems such as field order, insufficient support for Chinese word segmentation, frequent updates affect performance and large index space.

Aug 15, 2025 am 02:08 AM

What is the difference between INNER JOIN and OUTER JOIN in MySQL?

ThemaindifferenceisthatINNERJOINincludesonlyrowswithmatchesinbothtables,whileOUTERJOINincludesnon-matchingrowsfromoneorbothtables;specifically,LEFTJOINreturnsallrowsfromthelefttableandmatchedrowsfromtheright(withNULLsforunmatched),RIGHTJOINreturnsall

Aug 15, 2025 am 12:58 AM

How to drop a view in MySQL

To delete a view in MySQL, use the DROPVIEW statement; 1. The basic syntax is DROPVIEWview_name; 2. If you are not sure whether the view exists, you can use DROPVIEWIFEXISTSview_name to avoid errors; 3. You can delete multiple views at once through DROPVIEWIFEXISTSview1, view2, view3; the deletion operation only removes the view definition and does not affect the underlying table data, but you need to ensure that no other views or applications rely on the view, otherwise an error may be caused, and the executor must have DROP permissions.

Aug 14, 2025 pm 06:16 PM

mysql

How to use the COALESCE() function in MySQL?

COALESCE()returnsthefirstnon-NULLvaluefromalistofexpressions,enablinggracefulhandlingofmissingdatabysubstitutingdefaults,mergingcolumnvalues,supportingcalculationswithoptionalfields,andprovidingfallbacksinjoinsandaggregations,ensuringpredictableresul

Aug 14, 2025 pm 06:15 PM

What is the difference between UNION and UNION ALL in MySQL?

UNIONremovesduplicateswhileUNIONALLkeepsallrowsincludingduplicates;1.UNIONperformsdeduplicationbysortingandcomparingrows,returningonlyuniqueresults,whichmakesitsloweronlargedatasets;2.UNIONALLincludeseveryrowfromeachquerywithoutcheckingforduplicates,

Aug 14, 2025 pm 05:25 PM

mysql union

How to handle BLOB and TEXT data types in MySQL?

BLOB and TEXT are used to store large amounts of data. BLOB stores binary data, and TEXT stores text data. Each has four sizes: TINY, ordinary, MEDIUM, and LONG, with a maximum of 4GB; 1. BLOB/TEXT should be avoided for small data, and VARCHAR should be used instead to improve performance; 2. It is not advisable to store files directly in the database. It is recommended to store file paths and store files in the file system or cloud storage; 3. BLOB is used for true binary data, and text classes such as JSON/XML should be stored as TEXT to support character sets and debugging; 4. It is impossible to index the complete BLOB/TEXT, and you can create a prefix index such as CREATEINDEXidx_contentONartic

Aug 14, 2025 pm 04:58 PM