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Technical Articles

Database

Mysql Tutorial

How to fix 'Too many connections' error in MySQL

Checkmax_connectionsandThreads_connectedtoconfirmthelimitandcurrentusage.2.Increasemax_connectionstemporarilywithSETGLOBALorpermanentlyviamy.cnf/my.ini.3.Useconnectionpooling,closeconnectionsexplicitly,andmanagepersistentconnectionsintheapplication.4

Aug 08, 2025 am 11:37 AM

mysql Database Connectivity

How to manage foreign key constraints in MySQL

DefineforeignkeysduringtablecreationusingFOREIGNKEYwithREFERENCESandspecifyONDELETE/ONUPDATEactionslikeCASCADEtomaintainreferentialintegrity.2.AddforeignkeyconstraintstoexistingtablesviaALTERTABLEwithADDCONSTRAINT,ensuringmatchingcolumntypesandindexe

Aug 08, 2025 am 11:26 AM

How to show all databases in MySQL

To display all databases in MySQL, you need to use the SHOWDATABASES command; 1. After logging into the MySQL server, you can execute the SHOWDATABASES; command to list all databases that the current user has permission to access; 2. System databases such as information_schema, mysql, performance_schema and sys exist by default, but users with insufficient permissions may not be able to see it; 3. You can also query and filter the database through SELECTSCHEMA_NAMEFROMinformation_schema.SCHEMATA; for example, excluding the system database to only display the database created by users; make sure to use

Aug 08, 2025 am 09:50 AM

mysql database

How to perform a case-insensitive select in MySQL

Bydefault,MySQLperformscase-insensitiveSELECTqueriesduetocase-insensitivecollationslikeutf8mb4_general_ci;1.UseLOWER()orUPPER()functionstoconvertbothcolumnandsearchvaluetothesamecase,thoughthismayimpactindexusagewithoutfunctionalindexes;2.UseLIKE,whi

Aug 08, 2025 am 08:25 AM

How to troubleshoot MySQL replication issues

CheckreplicationstatususingSHOWSLAVESTATUS\G,verifyingSlave_IO_RunningandSlave_SQL_RunningareYes,inspectingLast_ErrorandSeconds_Behind_Masterforissues.2.ForSlave_IO_Running=No,resolveconnectionproblemsbyconfirmingmasterhost,port,credentials,networkac

Aug 08, 2025 am 08:15 AM

mysql copy

How to use the HAVING clause versus the WHERE clause in MySQL?

UseWHEREtofilterindividualrowsbeforegrouping,asitoperatesonrawdataandimprovesperformancebyexcludingunwantedrowsearly;2.UseHAVINGtofiltergroupsafteraggregation,asitworkswithaggregatefunctionslikeCOUNT()andAVG()thatarecalculatedafterGROUPBY;3.WHEREcann

Aug 08, 2025 am 08:05 AM

How to Monitor MySQL Performance and Identify Bottlenecks?

Enable slow query logs to identify queries that have been executed for too long. By setting slow_query_log, long_query_time, log_queries_not_using_indexes parameters, and using pt-query-digest to analyze the logs to optimize key queries; 2. Use PerformanceSchema and INFORMATION_SCHEMA to view the most time-consuming SQL statements, table I/O waiting and currently running queries, focusing on sessions that are in the "Sendingdata" or "Locked" state for a long time; 3. Monitor Threads_running and Innodb_r

Aug 08, 2025 am 06:51 AM

How to Troubleshoot Common MySQL Connection Errors?

Check whether the MySQL service is running, use sudosystemctlstatusmysql to confirm and start; 2. Make sure that bind-address is set to 0.0.0.0 to allow remote connections and restart the service; 3. Verify whether the 3306 port is open, check and configure the firewall rules to allow the port; 4. For the "Accessdenied" error, you need to check the user name, password and host name, and then log in to MySQL and query the mysql.user table to confirm permissions. If necessary, create or update the user and authorize it, such as using 'your_user'@'%'; 5. If authentication is lost due to caching_sha2_password

Aug 08, 2025 am 06:44 AM

mysql connection error

How to get the last inserted ID in MySQL

To get the last inserted ID in MySQL, use the LAST_INSERT_ID() function. 1. After executing the INSERT statement, you can directly call SELECTLAST_INSERT_ID() to get the last self-increment ID in the current session; 2. This function is session-safe and will not interfere with each other when multiple users concurrent operations; 3. Its value persists in the same connection until the next time the self-increment data is inserted; 4. Returns the valid ID only when inserting the table containing the AUTO_INCREMENT column, otherwise it will return 0; 5. In PHP, you can use the lastInsertId() method of PDO and cursor.lastro in Python.

Aug 08, 2025 am 06:26 AM

How to copy a table to another database in MySQL

Tocopybothstructureanddata,useCREATETABLE...LIKEfollowedbyINSERTINTO...SELECT,whichpreservesindexes,constraints,andAUTO_INCREMENTsettings.2.Tocopyonlythestructure,useCREATETABLE...LIKE,whichcreatesanemptytablewiththesameschema.3.Tocopystructureanddat

Aug 08, 2025 am 05:21 AM

How to prevent SQL injection in MySQL

Usepreparedstatementswithparameterizedqueriestotreatuserinputasdata,notexecutablecode.2.Validateandsanitizeinputbyfilteringdatatypes,limitinglength,andwhitelistingvalues.3.Escapeinputsonlyifpreparedstatementsarenotfeasible,usingfunctionslikereal_esca

Aug 08, 2025 am 05:09 AM

mysql sql injection

How to use GROUP_CONCAT in MySQL

GROUP_CONCAT is a function in MySQL that group multiple rows of data into strings by specified columns. 1. Basic splicing can be achieved through SELECTGROUP_CONCAT (column_name)FROMtable_nameGROUPBYgrouping_column; 2. Use SEPARATOR custom separators such as '|' or null values; 3. Use ORDERBYproductASC to sort the splicing contents within the function; 4. Use IFNULL or COALESCE to process NULL values; 5. Use SETSESSION or GLOBALgroup_concat_max_len

Aug 08, 2025 am 04:44 AM

mysql

Implementing MySQL Database Patch Management

There are three reasons why patch management cannot be ignored: First, MySQL version is updated frequently, and patches are mostly used to repair security vulnerabilities or known problems; second, failure to upgrade in time may cause the database to face the risk of attack or run abnormalities, such as master-slave replication failure; third, even if you use MySQL instances on the cloud, you still need to grasp the upgrade timing and scope of impact. Three key points should be considered when judging whether to patch: whether security vulnerabilities are involved need to be handled first; whether they affect current business functions; and whether they are major changes need to be carefully evaluated. Patch testing needs to be carried out in steps: build a test environment that is consistent with the production environment, back up data in advance, perform core SQL and stress tests, check logs and application layer compatibility. Suggestions for patch release: Choose business launch during the peak period and upgrade the slave first under the master-slave architecture

Aug 08, 2025 am 04:03 AM

mysql database

How to Deal with Deadlocks in MySQL?

Deadlock cannot be completely avoided, but can be effectively managed through the following measures: 1. Catch deadlock errors in application code (such as MySQL's 1213 error) and retry the transaction. It is recommended to use exponential backoff delay; 2. Shorten the time when the transaction holds locks, move non-database operations out of the transaction and commit as soon as possible; 3. Access tables and rows in a consistent order in all transactions to prevent loop waiting; 4. Use a lower isolation level (such as READCOMMITTED) when allowed to reduce the use of gap locks; 5. Optimize indexes to reduce lock contention, ensure that query conditions, connections and sort fields use appropriate indexes; 6. Use SELECT...FORUPDATE and LOCKINSHAREMODE with caution, lock only necessary rows

Aug 08, 2025 am 03:07 AM