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Technical Articles

Database

How does the LATENCY DOCTOR command work?

TheLATENCYDOCTORcommandisadiagnostictoolusedtoidentifyandanalyzesourcesoflatencyinreal-timesystems.1)ItcheckssubsystemslikeCPUscheduling,memoryaccess,networkstack,andhardwaredriversforbottlenecks.2)Theoutputincludessectionswithlatencyscoresindicating

Sep 08, 2025 am 03:24 AM

How to add a column to a table in MySQL?

To add columns to an existing table, you need to use the ALTERTABLE statement to the ADDCOLUMN clause; for example, ALTERTABLEusersADDCOLUMNemailVARCHAR(100) can add email columns to the users table; you can add constraints such as NOTNULL and DEFAULT at the same time, such as automatically recording time when creating a time column; you can specify the location of the column through FIRST or AFTER; support adding multiple columns at a time to improve efficiency; be careful when operating large tables to avoid locking tables affecting performance, and backup data should be backed up before modification. If you add non-empty columns, the default value must be set to prevent the operation from failing.

Sep 08, 2025 am 03:23 AM

mysql database

How to calculate the distance between two points using GEODIST?

GEODIST is a function used to calculate the straight line distance between two points on the earth. Before using it in Stata, it is required to install: sscinstallgeodist. 1. When using it, you need to specify the latitude and longitude parameters of the two points, such as geodistlat1lon1lat2lon2,gen(distance_km) to generate a unit distance of kilometers; 2. If you need a unit of miles, add the mile option; 3. Pay attention to ensuring that the latitude and longitude is in the decimal system format, the range is legal and the order of variables is correct; 4. During batch calculation, you can copy the reference point to all lines and execute the command. This method is suitable for store location selection, traffic analysis and other scenarios.

Sep 08, 2025 am 03:06 AM

distance calculation GEODIST

What is a NATURAL JOIN in MySQL?

ANATURALJOINinMySQLautomaticallyjoinstablesbasedoncolumnswiththesamenameandcompatibledatatypes,returningonlyonecopyofeachcommoncolumn;itrequiresnoexplicitONorUSINGclause,makingitconcisebutriskyduetoimplicitbehaviorthatcanleadtounexpectedresultsifsche

Sep 08, 2025 am 03:04 AM

mysql join

How to reconnect to a database?

The database connection suddenly disconnects can be checked according to the following steps: 1. Check whether the database service is running, use the systemctl or pg_ctl command for Linux, use the systemctl or pg_ctl command for Windows, and view the service manager for cloud database to view the console status of the cloud database; 2. Make sure that the connection parameters are correct, including the host address, port, user name, password and database name; 3. Check the network and permissions to ensure that the firewall releases the port, the user has remote access rights and correctly configure SSL; 4. Use the telnet or nc command for testing network connectivity; 5. Restart the application or reset the connection pool to clear the old connection.

Sep 08, 2025 am 02:56 AM

How to Use Partial Indexes to Optimize Queries in MongoDB

PartialindexesinMongoDBimproveperformancebyindexingonlydocumentsthatmatchaspecifiedcondition,reducingstorageandenhancingqueryspeed.TheyarecreatedusingthepartialFilterExpressionoption,suchasindexingemailsonlyforactiveusers:db.users.createIndex({email:

Sep 08, 2025 am 02:25 AM

mongodb

How to use user-defined variables in MySQL

User-defined variables start with @, and are assigned through SET or :=, which are only valid in the current session. They can be used to store values, simulate line numbers, etc. 1. Set variables using SET or SELECT; 2. Reference variables in subsequent statements; 3. Pay attention to the session scope and initialization, avoid undefined use, and finally end with a complete statement.

Sep 08, 2025 am 02:19 AM

How to connect to MySQL using Node.js

Install the mysql2 package: Run npminstallmysql2 to obtain a MySQL client with better performance and support Promise; 2. Create a connection: Use the mysql.createConnection() method and pass in the correct host, user name, password and database name to establish a connection; 3. Execute query: execute SQL statements through the connection.query() method and process the results; 4. Close the connection: Call the connection.end() method to safely close the connection; 5. Use Promise: Introduce the 'mysql2/promise' module to support async/await syntax to improve the readability of asynchronous operations

Sep 08, 2025 am 02:10 AM

How to Create and Manage Indexes in MongoDB

Indexesimprovequeryperformancebyreducingdocumentscans;createthemonfrequentlyqueriedfieldsusingcreateIndex(),monitorwithgetIndexes()andexplain(),andremoveunusedonestomaintainefficiency.

Sep 08, 2025 am 01:46 AM

How to trim whitespace from a string in SQL

UseTRIM()toremovebothleadingandtrailingwhitespace,LTRIM()forleadingonly,andRTRIM()fortrailingonly;thesefunctionsarewidelysupportedinPostgreSQL,MySQL,Oracle,SQLServer(2017 ),andrecentSQLite,withSQLServerbefore2017requiringLTRIM(RTRIM())andsomedatabase

Sep 08, 2025 am 01:36 AM

sql String processing

How to use the ROW_NUMBER function in SQL

ROW_NUMBER()assignsauniquesequentialnumbertoeachrowwithinaresultsetbasedonthespecifiedorder,anditcanalsorestartnumberingwithingroupsusingPARTITIONBY.1.Toassignsequentialnumberstoallrows,useROW_NUMBER()OVER(ORDERBYcolumn)torankrowsuniquely,evenwithdup

Sep 08, 2025 am 01:33 AM

How to create a new database in phpMyAdmin

AccessphpMyAdminbynavigatingtohttp://localhost/phpmyadminoryourhost’sprovidedURLandloginwithyourMySQLcredentials.2.Clickthe"Databases"tabinthetopmenu.3.Enteravaliddatabasenameinthe"Createdatabase"field,usingunderscoresinsteadofspa

Sep 08, 2025 am 01:04 AM

What is the information_schema database in MySQL?

information_schemaisaread-onlyvirtualdatabaseinMySQLthatprovidesmetadataaboutallotherdatabases;itcontainssystemviewslikeTABLES,COLUMNS,andSCHEMATAforqueryingdatabasestructure,enablingtaskssuchasfindingtableswithspecificcolumnsorlistingindexinformatio

Sep 08, 2025 am 12:57 AM

How to query a parent-child hierarchy in MySQL

MySQL supports querying parent-child hierarchy structures depending on the version: ① MySQL8.0 can use recursive CTE to traverse downwards (such as querying all subordinates of a manager) or trace upwards (such as the path from employees to CEO); ② Old versions need to use stored procedures to simulate recursion with temporary tables; ③ can load full data at the application layer to build a tree structure; ④ Optimization scheme includes using closure tables or path enumerations (such as storage /1/3/7/paths) to improve query performance, where path enumerations quickly obtain subtrees through LIKE matching, which is suitable for large-scale hierarchical data.

Sep 08, 2025 am 12:25 AM