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Technical Articles

Database

What is the MySQL event_scheduler and how to enable it?

TocheckiftheMySQLevent_schedulerisenabled,runSHOWVARIABLESLIKE'event_scheduler';possiblevaluesareON,OFF,orDISABLED.2.Toenableittemporarily,useSETGLOBALevent_scheduler=ON;thislastsuntilthenextrestart.3.Toenableitpermanently,addevent_scheduler=ONundert

Aug 07, 2025 am 03:30 AM

How do you delete records from a SQL table?

TodeleterecordsfromaSQLtable,usetheDELETEstatementwithaWHEREclausetospecifythecondition,asomittingitwilldeleteallrows.2.Multiplerecordscanbedeletedusingbroaderconditionswithoperatorslike>,IN,orLIKE,suchasDELETEFROMusersWHEREage>65.3.Toremoveall

Aug 07, 2025 am 01:41 AM

How to edit a record directly in the Navicat grid view?

You can edit data directly in Navicat's grid view, but the prerequisites must be met and followed by steps. 1. First make sure that you have entered the edit mode, click the "Edit" button of the toolbar or right-click to select "EditRecord"; 2. Click the cell in the grid view to modify the content, press Enter or switch the cell to confirm the changes, and double-click the selection option in the ENUM type field; 3. After modification, you must save it manually (Ctrl S or click the Save button), otherwise switching the tab will cause the changes to be lost; 4. If you cannot edit, possible reasons include no primary key on the table, insufficient user permissions, unupdated view or database type restrictions. The editing function is greatly affected by the table structure and permission settings, so you need to pay attention to these key points when operating.

Aug 07, 2025 am 01:31 AM

What security features does Navicat offer?

Navicatoffersmultiplebuilt-insecurityfeaturestoprotectdataandconnections.1.ItsupportsSSL/TLSencryptionforsecuredatabaseconnections,allowscertificateverification,andenablesenforcementofSSLmodes.2.Passwordsarestoredencrypted,accessisbasedonexistinguser

Aug 07, 2025 am 12:57 AM

How to connect to MySQL using Java with JDBC

ConnectingtoMySQLusingJavawithJDBCisacommontaskwhenbuildingJavaapplicationsthatinteractwithdatabases.Here'sastep-by-stepguidetohelpyouestablishaconnectionproperly.1.AddtheMySQLJDBCDriver(Connector/J)Beforeyoucanconnec

Aug 07, 2025 am 12:04 AM

MySQL Database Performance Tuning for Specific Workloads

Database performance tuning needs to be focused on business scenarios. 1. The OLTP scenario needs to increase innodb_buffer_pool_size, enable adaptive hash index, adjust log refresh strategy, use connection pools and design index reasonably; 2. The OLAP scenario should improve sorting and connection buffers, reasonably partition, use materialized views and optimize query statements; 3. InnoDB is recommended for writing multiple scenarios, adjust IO parameters, merge write operations, turn off automatic submission and monitor log files.

Aug 06, 2025 pm 06:07 PM

Optimizing MySQL for Customer Relationship Management (CRM)

TooptimizeMySQLperformanceforaCRMsystem,focusonindexingstrategies,schemadesignbalance,andqueryefficiency.1)Useproperindexingbyanalyzingfrequentqueries,addingindexesonWHEREclausecolumns,JOINkeys,andORDERBYfields,andconsideringcompositeindexeswheremult

Aug 06, 2025 pm 06:04 PM

mysql crm

How to use the COUNT function in MySQL

COUNT(*)countsallrowsincludingNULLs,COUNT(column)countsnon-NULLvalues,andCOUNT(DISTINCTcolumn)countsuniquenon-NULLvalues;usewithWHEREtofilter,GROUPBYtogroupresults,andHAVINGtofiltergroups,ensuringaccuratedataanalysisinMySQL.

Aug 06, 2025 pm 05:58 PM

How to set session variables in MySQL?

To set MySQL session variables, use the SETSESSION or SET commands; 1. Use SETSESSIONvariable_name=value; or abbreviated as SETvariable_name=value; both are equivalent; 2. Common examples include setting the time zone SETSESSIONtime_zone=' 00:00'; adjusting the maximum allowable packet size SETSESSIONmax_allowed_packet=67108864; and controlling automatic submission of SETSESSIONautocommit=0; 3. SET, SETSESSION and SETLOCAL are in the session

Aug 06, 2025 pm 05:46 PM

mysql

How to update data in a table in MySQL

To update data in MySQL table, you must use the UPDATE statement and ensure that the WHERE conditions are included to avoid accidental modification of all rows; 1. Update a single row: Modify a specific record with precise conditions (such as id=1); 2. Update multiple columns: Specify multiple columns and values in the SET clause; 3. Update multiple rows: Use conditions that match multiple records (such as email includes.com); 4. Use LIMIT to limit the number of rows to be updated (optional, commonly used for testing); 5. Security suggestions: Always backup data, test conditions with SELECT first, and use transactions for rollback; Common errors include omission of WHERE clauses, unclear conditions and unverified results; in short, be sure to operate with caution to ensure that the update is accurate and recoverable.

Aug 06, 2025 pm 05:18 PM

The Complete SQL Course: From Basic Queries to Advanced Database Management

StartwithbasicSELECTqueriesusingFROM,WHERE,ORDERBY,andLIMIT,andpracticefilteringwithDISTINCT,BETWEEN,IN,LIKE,andNULLhandling.2.Useaggregatefunctions(COUNT,SUM,AVG,MIN,MAX)withGROUPBYtosummarizedataandapplyHAVINGtofiltergroupedresults.3.Jointablesusin

Aug 06, 2025 pm 05:06 PM

Troubleshooting MySQL Service Unavailable Errors

The troubleshooting of MySQL service is not available requires the following steps. 1. First check whether the MySQL service is running, use systemctlstatusmysql to view the status, if it is not running, try to start, and view the error log if it fails; 2. Confirm the monitoring status of port 3306, check the firewall settings and adjust the bind-address configuration to allow remote access; 3. Check user permissions, grant remote access permissions by modifying the host field, and pay attention to security; 4. Troubleshoot insufficient resources or configuration errors, check memory and disk usage, adjust buffer pool parameters and restart the service. Gradually check the root cause of the problem in accordance with the above directions.

Aug 06, 2025 pm 05:05 PM

How to find columns with a specific data type in SQL?

To find columns with specific data types, you should query the metadata table of the database; 1. Use INFORMATION_SCHEMA.COLUMNS to query the specified data type and database name, which is suitable for MySQL, PostgreSQL, SQLServer, etc.; 2. PostgreSQL can use pg_catalog system table to obtain more detailed information; 3. SQLServer can obtain column and type information through sys.columns and sys.tables query; 4. MySQL can add CHARACTER_MAXIMUM_LENGTH and other conditions in INFORMATION_SCHEMA.COLUMNS.

Aug 06, 2025 pm 05:02 PM

sql type of data

What are constraints in SQL and why are they used?

ConstraintsinSQLareusedtoenforcedataintegrity,ensureaccuracy,andmaintainconsistencybypreventinginvaliddataentry.1.NOTNULLensuresacolumncannothavenullvalues;2.UNIQUEguaranteesallcolumnvaluesaredistinct;3.PRIMARYKEYcombinesNOTNULLandUNIQUEtouniquelyide

Aug 06, 2025 pm 05:01 PM