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Technical Articles

Database

Mysql Tutorial

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

How to clone a database in MySQL

Usemysqldumptoexportandimportthedatabaseforareliable,fullclone;2.UseCREATETABLE...LIKEandINSERTforcloningspecifictablesmanually;3.UseMySQLWorkbenchorphpMyAdminforaGUI-basedclone;4.Ensureproperpermissions,sufficientstorage,andhandleforeignkeysandlarge

Aug 30, 2025 am 12:28 AM

How to find duplicate values in a table in MySQL

To find duplicate values ??in MySQL table, you should use the GROUPBY and HAVING clauses; 1. Use SELECTemail,COUNT()AScountFROMusersGROUPBYemailHAVINGCOUNT()>1; to find duplicate mailboxes; 2. When expanding to multiple columns, use SELECTfirst_name,last_name,COUNT()AScountFROMusersGROUPBYfirst_name,last_nameHAVINGCOUNT()>1; to find duplicates based on multiple fields; 3. When looking for completely duplicate rows, all columns are performed

Aug 29, 2025 am 05:17 AM

How to use the CASE statement in MySQL?

There are two forms of CASE statements in MySQL: search type CASE and simple type CASE, among which search type is more commonly used; search type returns the corresponding results through the WHEN clause specified conditions, which are suitable for clauses such as SELECT, UPDATE, ORDERBY, etc., and can be used for data classification, custom sorting and condition update; simple type matches expressions with multiple values ??one by one and returns the result; CASE must end with END, ELSE is optional, but it is recommended to avoid NULL values; combined with aggregate functions, conditional statistics can be implemented, such as group counting with SUM (CASEWHEN...), thereby improving SQL's flexibility and functionality in data conversion and report generation.

Aug 29, 2025 am 04:33 AM

How to remove duplicate rows from a table in MySQL

Use the temporary table method to safely deduplicate. First create a temporary table with the same structure, insert the deduplicate data, rename the table and delete the backup; 2. MySQL8.0 can use the ROW_NUMBER() window function to mark duplicate rows, delete rows with a number greater than 1, and retain the first row sorted by the primary key; 3. Old version of MySQL can delete duplicates through self-connection, and retain rows with smaller ids; 4. Adding unique constraints can prevent future duplication. Before the operation, data must be backed up, queries must be tested first, and appropriate methods must be selected based on the MySQL version and primary key conditions. Temporary table method is the safest, and a unique index should be added to prevent duplicate data from appearing again.

Aug 29, 2025 am 03:59 AM

How to find circular references in foreign keys in MySQL

Circularreferencesinforeignkeyscancauseissueswithinserts,updates,anddeletes,especiallywithcascadingoperations.2.Theyoccurwhenachainofforeignkeyreferencesformsaloop,eitherdirectlyorindirectly.3.InMySQL8.0 ,usearecursiveCTEqueryonINFORMATION_SCHEMA.KEY

Aug 29, 2025 am 02:08 AM

How to deal with deadlocks in MySQL

MySQLautomaticallydetectsdeadlocksusingawait-forgraphandresolvesthembyabortingonetransaction,whichreceiveserror1213,whiletheotherproceeds;2.Applicationsmusthandletherollbackandretrythetransactionusingaretrymechanismwithlimitedattemptsandoptionalexpon

Aug 29, 2025 am 01:50 AM

How to configure a master-slave replication in MySQL

Configuring MySQL master-slave replication requires ensuring that the two servers are interconnected, version compatible, initial data consistent, and server-id is unique; 2. Enable binary logs on the master server and set server-id. After restarting MySQL, create a user with REPLICATIONSLAVE permission, and record the File and Position values ??output by SHOWMASTERSTATUS; 3. Configure the unique server-id on the slave server, enable relay-log, log-slave-updates and read-only, and execute CHANGEMASTERTO to specify the master server information and start STARTSL.

Aug 29, 2025 am 01:34 AM