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Technical Articles

Database

How to find circular references in a MySQL schema?

TofindcircularreferencesinaMySQLschema,querytheinformation_schematoextractforeignkeyrelationships,buildadirectedgraphoftabledependencies,andusecycledetectionalgorithmsorvisualizationtoolstoidentifyloops;specifically:1.Understandthatacircularreference

Aug 06, 2025 am 11:40 AM

What is the difference between the DELETE, TRUNCATE, and DROP commands in SQL?

DELETEremovesspecificrowsbasedonacondition,logseachdeletion,allowsrollback,andfirestriggers.2.TRUNCATEremovesallrowsquicklywithminimallogging,resetsauto-incrementcounters,doesnotfiretriggers,androllbacksupportdependsontheDBMS.3.DROPdeletestheentireta

Aug 06, 2025 am 11:16 AM

Troubleshooting Common MySQL Performance Bottlenecks

Common reasons for MySQL performance problems include improper index usage, slow query log not enabled, unreasonable table structure design and insufficient server resource configuration. 1. If you are slow inquiring, you must first check the index usage, analyze the execution plan through EXPLAIN, reasonably create composite indexes and avoid implicit conversions; 2. Turn on the slow query log and use tools to analyze "bad queries"; 3. Optimize the table structure to avoid abuse of large fields, unreasonable field types and excessive redundant fields; 4. Check the server configuration to ensure that memory, number of connections, and hard disk performance meet the needs, and can assist in the troubleshooting through monitoring tools.

Aug 06, 2025 am 11:15 AM

How do you perform implicit and explicit conversions in SQL?

SQL data type conversion is divided into implicit and explicit. 1. Implicit conversion is automatically executed by the database. For example, when comparing the string '100' with an integer, it may cause performance problems or errors; 2. Explicit conversion needs to be manually specified using functions such as CAST(), CONVERT() or TO_DATE(), such as CAST('2023-01-01'ASDATE), which can improve code reliability and portability; relying on implicit conversion should be avoided, especially during strings and days, and it is necessary to pay attention to conversion failures caused by invalid values. Always use explicit conversions to ensure accuracy and performance.

Aug 06, 2025 am 11:02 AM

What is the difference between SQL and NoSQL?

The core difference between SQL and NoSQL lies in design concepts, data structures, query languages, extension methods and applicable scenarios. 1. In terms of data structure, SQL adopts a tabular structure, which is suitable for scenarios with stable data models; while NoSQL supports various structures such as document type and key value type, which are suitable for scenarios with rapid iteration. 2. In terms of query language, SQL uses a unified standard SQL language, and the learning cost is fixed; while NoSQL lacks a unified language, such as MongoDB uses JSON format query, and there are great syntax differences. 3. In terms of scaling, SQL usually relies on vertical scaling, which is costly and has bottlenecks; while NoSQL supports horizontal scaling, suitable for large-scale data and high concurrency. 4. In terms of applicable scenarios, SQL is suitable for banking systems and other needs to be consistent

Aug 06, 2025 am 10:54 AM

What are some common date and time functions in SQL?

SQLprovidesbuilt-indateandtimefunctionsformanipulatingtemporaldata,withvariationsacrossdatabasesystems.1.CurrentdateandtimecanberetrievedusingNOW(),CURRENT_TIMESTAMP,GETDATE(),orSYSDATEdependingonthesystem.2.Datepartslikeyear,month,day,hour,etc.,aree

Aug 06, 2025 am 10:38 AM

sql datetime function

What are indexes in SQL and how do they improve performance?

IndexesinSQLsignificantlyimprovequeryperformancebyenablingfastdataretrievalthroughastructuredlookupmechanism.1)TheyallowthedatabasetoavoidfulltablescansbyusingdatastructureslikeB-treestoquicklylocaterowsmatchingaquerycondition.2)IndexesaccelerateSELE

Aug 06, 2025 am 09:55 AM

sql index

MySQL Database Release Management and Versioning

Using version control tools to record database changes, formulate clear release processes, pay attention to version compatibility and data migration, and recommend that CI/CD achieve automation is the key to doing a good job in MySQL database version management and release management. 1. It is recommended to use Liquibase or Flyway tools to record database changes, support automatic execution of upgrade scripts and cooperate with CI/CD; 2. The release process should include generation of change scripts in the development stage, testing environment verification, code review, pre-online inspection, execution of online and log recording; 3. When migrating data, it is necessary to ensure forward compatibility, migration in batches and retain old fields; 4. Include database changes in CI/CD to realize automated deployment and testing, and improve release efficiency and change controllability.

Aug 06, 2025 am 09:32 AM

How to apply a patch in Oracle?

Back up the database and OracleHome and verify patch compatibility, check the README file, stop the relevant processes, ensure sufficient disk space, set environment variables correctly, and confirm that the OPatch version is latest; 2. Download the patch from MyOracleSupport and unzip it to a temporary directory; 3. Use optchlsinventory to check the OracleHome and inventory status, and confirm the current ORACLE_HOME; 4. After entering the patch directory, use the optchapply command to apply the patch. The RAC environment needs to use the -rolling parameter to implement rolling applications; 5. If you need to perform the next steps, run the catchl.pl or datapatch tool

Aug 06, 2025 am 07:59 AM

MongoDB for Big Data Applications

MongoDB is suitable for big data due to flexible schema, horizontal scaling, high write throughput, aggregation analysis and ecological integration; 2. It is suitable for multi-source heterogeneous data storage, real-time write and query, and dynamic schema changes; 3. It is not suitable for strong transactions, complex association queries and rebatch scenarios, and should be used as a link of the hierarchical architecture rather than a full-stack solution.

Aug 06, 2025 am 07:36 AM

How to use IF() and IFNULL() functions in MySQL queries?

The IF() function is used for conditional logic in MySQL, and returns true or false values according to conditions, such as converting order states 0 and 1 into "Pending" and "Completed"; 2. The IFNULL() function is used to process NULL values. If the expression is NULL, it returns a specified alternative value, which is often used to display empty discounts as 0; 3. You can use IF() and IFNULL() to implement complex logic, such as checking whether the mailbox exists first and then judging the verification status; 4. These functions are suitable for clauses such as SELECT and WHERE, but it should be noted that using in WHERE may affect index performance; 5. IF() and IFNULL() are MySQL-specific functions, providing concise conditional judgment and null value processing

Aug 06, 2025 am 07:16 AM

How to use GROUP BY to aggregate data in SQL?

ToeffectivelyuseSQL'sGROUPBYforsummarizingdata,alwayspairitwithaggregatefunctionslikeSUM,COUNT,orAVG,andensurenon-aggregatedcolumnsinSELECTareincludedinGROUPBY.1)UseGROUPBYtocollapserowswithmatchingvaluesintosummaryrows.2)Combinewithaggregatefunction

Aug 06, 2025 am 06:27 AM

MySQL Database Cloning for Development and Testing

The methods of directly copying production databases to the development and testing environment include: 1. Export and import using mysqldump, suitable for small and medium-sized databases, simple operation but slow speed; 2. Use physical file copying tools such as PerconaXtraBackup, suitable for large data volumes and does not affect online services; 3. Use MySQL8.0's CLONEPLUGIN to achieve remote cloning, suitable for automated deployment; at the same time, attention must be paid to data desensitization and access rights control to ensure security.

Aug 06, 2025 am 06:03 AM

What is an Oracle synonym?

AnOraclesynonymisanaliasforadatabaseobjectlikeatable,view,orprocedure,usedtosimplifySQLqueriesandmanageaccess.1)Synonymseliminatetheneedtoprefixobjectnameswiththeschemaowner(e.g.,usingempinsteadofhr.employees).2)Theyimproveapplicationportabilityacros

Aug 06, 2025 am 05:36 AM