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Technical Articles

Database

Mysql Tutorial

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

How to configure the query cache in MySQL

MySQL's query cache is only available in version 5.7 and earlier, and version 8.0 and above has been removed; 1. Confirm support through SHOWVARIABLESLIKE'have_query_cache' and check query_cache_type, query_cache_size, etc. configurations; 2. Set query_cache_type=ON, query_cache_size=256M, query_cache_limit=2M, query_cache_min_res_unit=512K in my.cnf to enable and optimize cache; 3. Use SHOWSTATUSLIKE

Aug 14, 2025 pm 03:31 PM

How to restart the MySQL server from the command line?

UsesudosystemctlrestartmysqlorsudosystemctlrestartmysqldonmodernLinuxsystemswithsystemd.2.UsesudoservicemysqlrestartorsudoservicemysqldrestartonolderLinuxsystems.3.Usesudo/etc/init.d/mysqlrestartfordirectscript-basedrestarts.4.OnmacOSwithHomebrew,use

Aug 14, 2025 pm 03:27 PM

How to execute a script file from the mysql command-line

ToexecuteascriptfilefromtheMySQLcommand-line,usetheSOURCEcommandor\.shortcutwithinMySQL,orrunitfromtheOScommandline.1.UseSOURCE/path/to/script.sql;inMySQLafterlogginginandselectingthedatabaseifneeded.2.Alternatively,use\./path/to/script.sqlasashortha

Aug 14, 2025 pm 02:44 PM

Automating MySQL Backups to AWS S3 or Google Cloud Storage

To automate backup of MySQL to AWSS3 or GoogleCloudStorage, you need to create backup scripts, upload backups, automate them with cron, and clean old files. 1. Create a mysqldump script containing database credentials and timestamps to generate backup files; 2. Use AWSCLI or gsutil tools to upload backups to S3 or GCS; 3. Automatically execute scripts and record logs through cron timing tasks every day at 2 a.m.; 4. Add cleaning commands to regularly delete old backups 7 days ago to save storage space. The entire process ensures that data is secure, automatic and recoverable.

Aug 14, 2025 pm 02:11 PM

How to find the median value in a MySQL column

UseROW_NUMBER()andCOUNT()OVER()torankrowsandgettotalcount;2.Filterrowswhererow_numequalsthemiddlepositionsusingFLOOR((total_count 1)/2)andCEIL((total_count 1)/2);3.WraptheresultandtakeAVG(amount)tocomputethemedian,whichworksforbothoddandevenrowcounts

Aug 14, 2025 pm 02:03 PM

How to find duplicate values in a MySQL table?

Tofindduplicatesinasinglecolumnlikeemail,useGROUPBYwithHAVINGCOUNT()>1toshowvaluesappearingmorethanonce.2.Forduplicatesacrossmultiplecolumnssuchasfirst_nameandlast_name,applyGROUPBYonthecombinedcolumnswithHAVINGCOUNT()>1.3.Todisplayallduplicate

Aug 14, 2025 pm 02:02 PM

What are the different storage engines in MySQL?

InnoDB is MySQL default storage engine, suitable for applications that require transactions, high concurrency and data integrity, and supports row-level locks, foreign keys and crash recovery; MyISAM is suitable for read-intensive non-transactional scenarios but is no longer recommended; Memory engine is used for temporary data storage in memory, fast but not durable; CSV is used for data exchange, Archive is suitable for appended log data; Blackhole is used for testing and replication, NDB is used for high availability cluster environments, Federated is used for accessing remote tables, and Merge is the deprecated MyISAM merge engine. The selection engine should be based on specific needs. InnoDB is suitable for most modern applications.

Aug 14, 2025 pm 01:47 PM