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Technical Articles

Database

Mysql Tutorial

How to use the BETWEEN operator in MySQL

BETWEEN is an operator in MySQL used to filter data within a specified range and contains boundary values; 1. When used in numbers, such as salaryBETWEEN30000AND50000, equivalent to >= and

Aug 31, 2025 am 07:15 AM

mysql between

How to drop a temporary table in MySQL

To delete temporary tables in MySQL, you must use the DROPTEMPORARYTABLE statement; 1. You must include the TEMPORARY keyword to explicitly specify that the deleted temporary table is specified, otherwise MySQL will try to find a permanent table with the same name, which may cause an error; 2. Use DROPTEMPORARYTABLEtable_name; syntax to delete existing temporary tables, such as DROPTEMPORARYTABLEtemp_users; 3. To avoid errors when the table does not exist, you should add IFEXISTS clauses, such as DROPTEMPORARYTABLEIFEXISTStemp_users; 4. Temporary tables are only in the current session

Aug 31, 2025 am 06:43 AM

How to calculate the difference between two dates in MySQL

To calculate the difference between two dates in MySQL, the function should be selected according to the required units: 1. Use DATEDIFF() to obtain the difference in the number of days, such as DATEDIFF('2025-04-05','2025-03-01') to return 35, the function only compares the date part and the result symbol depends on the order; 2. Use TIMESTAMPDIFF() to obtain the difference in other units, such as TIMESTAMPDIFF(MONTH,'2025-03-01','2025-04-05') to return 1, supporting units such as YEAR, QUARTER, MONTH, DAY, HOUR, MINUTE, SECOND, etc.; 3. It can be calculated by direct subtraction but

Aug 31, 2025 am 06:08 AM

How to restore a database from a backup in MySQL

Torestorefromamysqldumpfile,firstcreatethedatabaseifitdoesn’texistusingCREATEDATABASEIFNOTEXISTSyour_database_name,thenrunmysql-uusername-pyour_database_name

Aug 31, 2025 am 05:52 AM

What is the innodb_file_per_table option in MySQL?

Theinnodb_file_per_tableoptionshouldbeenabledtoalloweachInnoDBtabletohaveitsown.ibdfile,improvingspacereclamation,manageability,andstorageoptimization,withbenefitsoutweighingminorfilesystemoverhead,anditisenabledbydefaultinMySQL5.6andlaterversions.

Aug 31, 2025 am 04:30 AM

mysql innodb

How to compare and synchronize two MySQL databases?

Compareschemasusingmysqldumpwith--no-dataanddiffortoolslikept-schema-sync;2.CompareandsyncdatausingCHECKSUMTABLE,SELECTCRC32withGROUP_CONCAT,orpreferablypt-table-checksumandpt-table-syncforaccuracy;3.AutomatewithMySQLreplication,customscriptsusingPyt

Aug 31, 2025 am 03:30 AM

How to grant permissions on a specific database only in MySQL

TograntpermissionsonaspecificdatabaseonlyinMySQL,usetheGRANTstatementwiththedatabasenameexplicitlyspecified.1.SpecifythedatabaseintheGRANTstatementusingtheformat:GRANTpermission_typeONdatabase_name.TO'username'@'host';forexample,GRANTALLPRIVILEGESONs

Aug 31, 2025 am 02:20 AM

What are the Best Practices for Naming Tables and Columns in MySQL?

Usedescriptiveandmeaningfulnamesfortablesandcolumnstoenhanceclarityandmaintainability.2.Adoptsnake_casewithunderscoresforalltableandcolumnnamestoensurereadabilityandcompatibilityacrosssystems.3.Prefersingulartablenames(e.g.,user,order)torepresententi

Aug 31, 2025 am 01:58 AM

mysql 數(shù)據(jù)庫命名

How to connect to MySQL using PHP with mysqli

To use PHP's mysqli extension to connect to MySQL, it is recommended to use object-oriented methods: 1. Create a mysqli instance and pass it in the host, username, password and database name; 2. Check connect_error to ensure the connection is successful; 3. Use environment variables to store credentials and log errors instead of direct output; 4. Close the connection in time after the connection is completed; 5. Enable SSL and preprocessing statements to prevent SQL injection; 6. Check permissions, MySQL service status, firewall and host configuration when the connection fails. After correct configuration, you can perform database operations through mysqli_query or preprocessing statements. After successful connection, "Connected successfully" should be displayed.

Aug 30, 2025 am 08:48 AM

mysql php

How to use LAG() and LEAD() functions in MySQL

MySQL's LAG() and LEAD() functions can be used to access data from the previous or next row in the result set. 1. The LAG() function is used to obtain the row value of the specified offset before the current row. It is often used to compare the difference between the current row and the previous row, such as calculating monthly income changes; 2. The LEAD() function obtains the subsequent row value, which is suitable for predicting or comparing future values; 3. Both must be used in conjunction with the OVER() clause, and supports PARTITIONBY processing data by group partition, and is available since MySQL8.0. When using it, you need to ensure version compatibility, and finally achieve inter-row calculations without self-connection.

Aug 30, 2025 am 07:13 AM

mysql Window Functions

MySQL Database Testing Methodologies and Tools

To effectively test MySQL databases, unit testing, integration testing, use testing tools and performance stress testing should be used. 1. Unit testing: Verify the correctness of SQL statements and stored procedures through frameworks such as unittest or JUnit, and combine Mock data and transaction control to ensure a clean test environment. 2. Integration testing: Simulate real business scenarios, verify the interaction between the application and the database, use independent test databases and cooperate with slow query monitoring to improve efficiency. 3. Use MySQLWorkbench, DBeaver, dbForgeStudio and other tools to assist in testing to improve automation level and test coverage. 4. Performance and stress testing: Simulation of high concurrency using Sysbench and JMeter

Aug 30, 2025 am 06:20 AM

mysql database Test Methods

How to optimize COUNT(*) for large tables in MySQL?

UseapproximatecountsfromSHOWTABLESTATUSorEXPLAINwhenprecisionisn’tneeded,astheyprovidefastestimateswithoutfullscans.2.Maintainacountertableupdatedviatriggersorapplicationlogicforexactcounts,enablinginstantretrieval.3.CachecountresultsinRedisortheappl

Aug 30, 2025 am 01:50 AM

What is the CONCAT_WS() function in MySQL?

CONCAT_WS()inMySQLconcatenatesstringswithaspecifiedseparator,ignoringNULLvalueswhileapplyingtheseparatoronlybetweennon-NULLvalues;1.Thefunctionusesaseparator(e.g.,',','-')placedbetweeneachpairofnon-NULLarguments;2.IftheseparatorisNULL,theentireresult

Aug 30, 2025 am 01:35 AM

How to handle errors in MySQL stored procedures?

Use the DECLAREHANDLER statement to effectively handle errors in MySQL stored procedures, and to deal with exceptions such as SQLEXCEPTION by defining a processor of CONTINUE or EXIT type. Combined with GETDIAGNOSTICS to obtain error details, and use transactions and OUT parameters to ensure the integrity of operations and the accuracy of feedback, thereby improving the robustness of database applications.

Aug 30, 2025 am 12:50 AM

mysql stored procedure