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- What is the CONCAT_WS() function in MySQL?
- CONCAT_WS()inMySQLconcatenatesstringswithaspecifiedseparator,ignoringNULLvalueswhileapplyingtheseparatoronlybetweennon-NULLvalues;1.Thefunctionusesaseparator(e.g.,',','-')placedbetweeneachpairofnon-NULLarguments;2.IftheseparatorisNULL,theentireresult
- Mysql Tutorial . Database 155 2025-08-30 01:35:01
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- 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.
- Mysql Tutorial . Database 862 2025-08-30 00:50:02
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- How to clone a database in MySQL
- Usemysqldumptoexportandimportthedatabaseforareliable,fullclone;2.UseCREATETABLE...LIKEandINSERTforcloningspecifictablesmanually;3.UseMySQLWorkbenchorphpMyAdminforaGUI-basedclone;4.Ensureproperpermissions,sufficientstorage,andhandleforeignkeysandlarge
- Mysql Tutorial . Database 185 2025-08-30 00:28:01
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- 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
- Mysql Tutorial . Database 946 2025-08-29 05:17:01
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- 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.
- Mysql Tutorial . Database 516 2025-08-29 04:33:01
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- 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.
- Mysql Tutorial . Database 854 2025-08-29 03:59:00
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- How to find circular references in foreign keys in MySQL
- Circularreferencesinforeignkeyscancauseissueswithinserts,updates,anddeletes,especiallywithcascadingoperations.2.Theyoccurwhenachainofforeignkeyreferencesformsaloop,eitherdirectlyorindirectly.3.InMySQL8.0 ,usearecursiveCTEqueryonINFORMATION_SCHEMA.KEY
- Mysql Tutorial . Database 221 2025-08-29 02:08:00
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- How to deal with deadlocks in MySQL
- MySQLautomaticallydetectsdeadlocksusingawait-forgraphandresolvesthembyabortingonetransaction,whichreceiveserror1213,whiletheotherproceeds;2.Applicationsmusthandletherollbackandretrythetransactionusingaretrymechanismwithlimitedattemptsandoptionalexpon
- Mysql Tutorial . Database 847 2025-08-29 01:50:00
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- 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.
- Mysql Tutorial . Database 355 2025-08-29 01:34:01
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- How to handle foreign key constraints in MySQL?
- ForeignkeyconstraintsinMySQLmaintainreferentialintegritybyensuringvalidrelationshipsbetweentables;theyaredefinedeitherduringtablecreationorviaALTERTABLE,canincludereferentialactionslikeCASCADEorSETNULL,andshouldbecarefullymanagedtopreventdatainconsis
- Mysql Tutorial . Database 230 2025-08-29 00:25:00
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- What is the max_connections setting in MySQL?
- max_connectionsinMySQLsetsthemaximumnumberofsimultaneousclientconnectionstheservercanhandle,withatypicaldefaultof151.1)ThevalueisadjustableviaconfigurationfileordynamicallyusingSETGLOBALmax_connections.2)Increasingitrequiressufficientsystemresourcesl
- Mysql Tutorial . Database 340 2025-08-28 08:19:01
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- How to pivot a table in MySQL
- MySQL does not have a built-in PIVOT operator, but it can be combined with GROUPBY through CASE statements; 1. Understand the basic structure: use SUM (CASEWHEN) for each column conditional aggregation; 2. Use SUM or MAX: use SUM for multiple rows, and use MAX for a single row to avoid addition; 3. Dynamic row to column: When the column value is unknown, use GROUP_CONCAT to generate dynamic SQL and execute it; 4. Best practices: reasonably alias, handle null values, use MAX for text, and optimize indexes; 5. Text data examples: use MAX (CASE) to extract non-numeric fields; static or dynamic row to column can be flexibly implemented through conditional aggregation, and finally use GROUPBY to complete the data rotation, fully implement the row to column function.
- Mysql Tutorial . Database 187 2025-08-28 08:06:01
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- What is AUTO_INCREMENT in MySQL?
- AUTO_INCREMENTinMySQLautomaticallygeneratesauniqueintegerforacolumn,typicallyusedforprimarykeys,ensuringeachnewrowreceivesasequentialidentifierwithoutmanualinput;itrequiresthecolumntobeaninteger,NOTNULL,andindexed,allowsonlyonepertable,incrementsfrom
- Mysql Tutorial . Database 328 2025-08-28 07:35:00
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- How to set up SSL/TLS for secure MySQL connections
- CheckSSLstatususingSHOWVARIABLESLIKE'%ssl%';ensurehave_sslisYESandssl_ca,ssl_cert,ssl_keypointtovalidfiles;verifyconnectionwithSHOWSTATUSLIKE'Ssl_cipher';2.GenerateSSLcertificatesusingOpenSSLbycreatingaCAwithopensslgenrsaandopensslreq,thengenerateser
- Mysql Tutorial . Database 1023 2025-08-28 06:45:01
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