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Technical Articles

Database

Mysql Tutorial

What are ACID properties in MySQL transactions?

ACIDpropertiesinMySQLtransactionsareAtomicity,Consistency,Isolation,andDurability,whichtogetherensurereliableandconsistentdatabaseoperations.Atomicityguaranteesthatalloperationswithinatransactionaretreatedasasingleunit,eitherfullycompletedorfullyroll

Aug 17, 2025 am 10:52 AM

What are the Different Types of Joins in MySQL and When to Use Them?

INNERJOINretrievesonlymatchingrowsfrombothtables,usedwhenyouneeddatathatexistsinbothtables;2.LEFTJOINreturnsallrowsfromthelefttableandmatchedrowsfromtheright,withNULLsfornon-matches,idealforincludingallprimaryrecords;3.RIGHTJOINreturnsallrowsfromther

Aug 17, 2025 am 10:07 AM

What is the difference between REAL, DOUBLE, and FLOAT in MySQL?

REALisasynonymforDOUBLEbydefault,butcanactasFLOATifREAL_AS_FLOATSQLmodeisenabled;FLOATuses4byteswith~7-digitprecisionforsingle-precisionvalues,DOUBLEuses8byteswith~15–17-digitprecisionfordouble-precisionvalues,andREAL’sbehaviordependsonSQLmode,making

Aug 17, 2025 am 09:53 AM

mysql type of data

How to handle errors in MySQL stored procedures

UseDECLARECONTINUEorDECLAREEXITHANDLERtospecifyerrorhandlingbehavior,whereCONTINUEallowsexecutiontoproceedafterhandlingtheerror,andEXITstopsexecutionofthecurrentblock;2.HandleerrorsusingSQLSTATEvalues(e.g.,'23000'forconstraintviolations),MySQLerrorco

Aug 17, 2025 am 06:50 AM

mysql stored procedure

How to create a database in MySQL

To create a database using the MySQL command line, you must first log in and execute CREATEDATABASEdatabase_name; for example, CREATEDATABASEmy_first_db; 2. You can verify that the database was created successfully through SHOWDATABASES, and then use USEmy_first_db; select the database; 3. It is recommended to set character sets and collation: CREATEDATABASEmy_first_dbCHARACTERSETutf8mb4COLLATEutf8mb4_unicode_ci; 4. To create a database in phpMyAdmin, you must open the web interface and enter the data

Aug 17, 2025 am 06:33 AM

How to manage character encoding issues like utf8mb4 in MySQL?

To properly handle character encoding issues in MySQL, utf8mb4 must be used to support full UTF-8 characters such as emoji and 4-byte Unicode. 1. Use the utf8mb4 character set and utf8mb4_unicode_ci collation when creating or modifying the database; 2. Update the encoding of existing tables and columns to utf8mb4 through the ALTERTABLE and MODIFY commands; 3. Set the default character set of client, mysql and mysqld parts to utf8mb4 in the MySQL configuration file, and enable character-set-client-handshake=FALSE; 4.

Aug 17, 2025 am 04:52 AM

How to reset the root password in MySQL

StoptheMySQLserviceusingtheappropriatecommandforyoursystem.2.StartMySQLinsafemodewith--skip-grant-tablesand--skip-networkingtodisableauthenticationandremoteaccess.3.ConnecttoMySQLasrootwithoutapassword.4.ResettherootpasswordusingALTERUSERforMySQL5.7.

Aug 17, 2025 am 04:36 AM

How to work with date and time functions in MySQL?

MySQLsupportsDATE,TIME,DATETIME,TIMESTAMP,andYEARdatatypesforhandlingdateandtimevalues,withfunctionslikeNOW(),CURDATE(),andCURTIME()toretrievecurrentdateandtime,extractionfunctionssuchasYEAR(),MONTH(),andDAYNAME()toobtainspecificparts,DATE_FORMAT()fo

Aug 17, 2025 am 04:27 AM

mysql datetime function

How to create a function in MySQL

Tocreateauser-definedfunctioninMySQL,usetheCREATEFUNCTIONstatementwithpropersyntaxandDELIMITER.2.Definethefunctionwithaname,parameters,returntype,andcharacteristicslikeDETERMINISTICorREADSSQLDATA.3.WritethefunctionlogicwithinBEGIN...ENDblock,ensuring

Aug 17, 2025 am 02:54 AM

Optimizing MySQL for Large-Scale User Registrations

Tohandlelarge-scaleuserregistrationsinMySQL,useInnoDBasthestorageengineforrow-levellockingandcrashrecovery,avoidMyISAMduetotable-levellocking,enableinnodb_file_per_tableforeasiermanagement,andusefastdiskslikeSSDsorNVMe.Optimizetheschemabykeepingtheus

Aug 17, 2025 am 01:32 AM

What is the difference between CHAR and VARCHAR in MySQL?

CHAR is a fixed length, VARCHAR is a variable length; CHAR will fill the specified length with spaces and may waste spaces, while VARCHAR only uses the actual required space and retains the tail spaces; CHAR is up to 255 characters, VARCHAR can reach 65535; usually short and fixed length use CHAR, and variable length use VARCHAR.

Aug 17, 2025 am 01:27 AM

How to write a loop in a MySQL stored procedure

MySQLstoredproceduressupportthreelooptypes:1.WHILEcheckstheconditionbeforeeachiteration,makingitidealforuncertainiterationcounts;2.REPEATexecutesatleastonceandcheckstheconditionafterward;3.LOOPprovidesmanualcontrolusingLEAVEtoexitandITERATEtoskiptoth

Aug 17, 2025 am 12:10 AM

cycle

How to find tables with a specific column name in MySQL?

To find a table containing a specific column name, you should query the INFORMATION_SCHEMA.COLUMNS table; execute SELECTTABLE_NAMEFROMINFORMATION_SCHEMA.COLUMNSWHERECOLUMN_NAME='your_column_name'ANDTABLE_SCHEMA='your_database_name'; you can find all tables containing that column in the specified database, such as looking for tables containing an email column in sales_db; to search across all databases, omit the TABLE_SCHEMA condition and select to return TABLE_NAME at the same time.

Aug 16, 2025 am 11:29 AM

How to pivot data in MySQL (rows to columns)?

To implement row-to-column conversion (i.e. pivot table) in MySQL, conditional aggregation is required to be combined with GROUPBY; 1. Use SUM (CASE...) or MAX (CASE...) combined with GROUPBY to convert row data into columns, which is suitable for known column values; 2. When the column value is not fixed, dynamic SQL is generated through GROUP_CONCAT and executed with PREPARE, pay attention to adjusting group_concat_max_len; 3. IF can be used to replace CASE to simplify syntax, but CASE is still recommended; always use aggregate function, missing values are filled with 0 or NULL, text data is MAX instead of SUM, and finally perspective is completed through grouping and conditional logic.

Aug 16, 2025 am 10:54 AM