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Home

Technical Articles

Database

How to create and manage schemas in SQL?

Create a pattern: Use CREATESCHEMAschema_name to create a pattern in PostgreSQL or SQLServer. In MySQL, CREATEDATABASEschema_name is equivalent to creating a pattern; 2. Create a table in the pattern: Use CREATETABLEschema_name.table_name to define the table structure, such as CREATETABLEmarketing.campaigns; 3. Set the search path: execute SETsearch_pathTOmarketing and public in PostgreSQL to prioritize finding the marketing pattern.

Sep 02, 2025 am 07:59 AM

How to find all leaf nodes in a tree structure in MySQL

Inanadjacencylistmodel,leafnodesarefoundusingaLEFTJOINtoidentifynodeswithoutchildren:SELECTt1.id,t1.nameFROMtreet1LEFTJOINtreet2ONt1.id=t2.parent_idWHEREt2.parent_idISNULL;2.Inanestedsetmodel,leafnodesareidentifiedwherergt=lft 1:SELECTid,nameFROMtree

Sep 02, 2025 am 07:51 AM

How to handle data type conversion errors in SQL

TopreventdatatypeconversionerrorsinSQL,usesafeconversionfunctionslikeTRY_CAST(),TRY_CONVERT(),orconditionallogicwithvalidationcheckstoreturnNULLinsteadoferrors;validatedataformatsbeforeconversionusingregexorbuilt-infunctions;handleedgecaseswithCASEst

Sep 02, 2025 am 07:50 AM

sql Data type conversion

How to Import and Export Data from a CSV File in MySQL?

ToexportdatatoaCSV,useSELECT...INTOOUTFILEwithproperpath,field,andlineformatting,ensuringtheMySQLuserhasFILEprivilegeandtheservercanwritetothespecifiedlocation;2.ToimportdatafromaCSV,useLOADDATAINFILEwithmatchingtablestructureandfielddefinitions,usin

Sep 02, 2025 am 06:47 AM

How to find the last inserted ID in MySQL?

TofindthelastinsertedIDinMySQL,usetheLAST_INSERT_ID()functionimmediatelyaftertheINSERTstatement;1.Itreturnstheauto-generatedIDfromthemostrecentINSERTinthecurrentsession;2.Itissession-specific,ensuringsafetyinmulti-userenvironments;3.Itpersistsuntilan

Sep 02, 2025 am 06:12 AM

How can you monitor the health and performance of a MongoDB deployment?

The key to monitoring MongoDB's health and performance lies in mastering core metrics and using tools reasonably. First, you need to pay attention to system resources, including CPU usage, memory usage, disk I/O and network traffic, and use top, htop, iostat or Prometheus Grafana to monitor; secondly, use MongoDB's own commands such as db.currentOp(), db.serverStatus(), db.collection.stats() and rs.status() to quickly understand the database status; then configure automated monitoring tools such as MongoDBAtlas, Prometheus MongoDBExporter,

Sep 02, 2025 am 06:06 AM

mongodb Performance monitoring

How to compare backup file contents?

To view and compare the content of the backup file, you can follow the following steps: 1. Use decompression tools such as WinRAR or tar command to view the backup structure; 2. Compare the file list and size of the two backups, and use scripts to extract and diff comparison; 3. Extract key files such as dump.sql or config.php, and use text comparison tools to check the content differences; 4. Use special tools such as WinMerge, KDiff3 or rsync for in-depth analysis to ensure comprehensive and accurate identification of changes.

Sep 02, 2025 am 05:52 AM

How to customize Code Completion suggestions?

If you want to make code completion more suitable for your habits, you can do it in the following ways: 1. Adjust the built-in settings of the IDE, including modifying the length of the trigger keyword, adjusting the priority strategy, and closing the prompts for the feature of infrequent languages; 2. Use plug-ins/extensions to enhance capabilities, such as the combination of Tabnine, GitHubCopilot and Prettier IntelliSense plug-in, and configure behavioral preferences; 3. Customize Snippet to improve efficiency, add commonly used code snippets to quickly expand the code. By gradually optimizing these settings, the intelligence and personalization of code completion can be improved, thereby better matching personal development habits.

Sep 02, 2025 am 05:11 AM

How to insert data into a MySQL table?

Use the INSERTINTO statement to insert data into the MySQL table. The basic syntax is INSERTINTOtable_name(column1,column2,...)VALUES(value1,value2,...). You can insert a single row, multiple rows, or insert data from other table query results. For example, INSERTINTOusers(name,email,age)VALUES('JohnDoe','john@example.com',30) to insert a single record, or you can use INSERTINTOusers(name,email,age)VALUES(...),(..

Sep 02, 2025 am 04:04 AM

mysql Data insertion

How to drop a function in MySQL

To delete functions in MySQL, use the DROPFUNCTION statement; 1. Specify the function name: DROPFUNCTIONfunction_name; 2. Optional IFEXISTS to prevent error reporting: DROPFUNCTIONIFEXISTS function_name; 3. Make sure to have ALTERROUTINE permission; 4. Check whether there is a dependency before deletion; 5. You can view existing functions by querying INFORMATION_SCHEMA.ROUTINES; be careful when executing to avoid affecting the production environment.

Sep 02, 2025 am 03:54 AM

mysql

How to find the Nth highest salary in SQL?

UseLIMITOFFSETwithDISTINCTforsimplecasesinMySQL/PostgreSQL,ensuringduplicatesarehandledbyskippingN-1rowsandfetchingthenextuniquesalary.2.ApplyROW_NUMBER()inmodernSQLdatabaseswhenstrictrownumberingisneeded,butnoteitassignsdifferentrankstoduplicatesala

Sep 02, 2025 am 03:10 AM

How to convert an integer to a string in SQL?

To convert integers into strings, you should choose the appropriate method according to the database system: 1. Use CAST() function, such as SELECTCAST(123ASVARCHAR(10)), which complies with the ANSISQL standard and is suitable for PostgreSQL, SQLServer, MySQL, Oracle and SQLite, etc., with the best cross-database compatibility; 2. Use CONVERT() function, such as SELECTCONVERT(VARCHAR(10), 123), which is mainly used for SQLServer and MySQL, supports format conversion, but the syntax varies from database to database; 3. Database-specific functions include Oracle's TO_CHA

Sep 02, 2025 am 03:02 AM

What is the SUBSTRING_INDEX() function in MySQL?

SUBSTRING_INDEX()extractsasubstringfromastringbasedonadelimiterandoccurrencecount,returningtheportionbeforethespecifiednumberofdelimiteroccurrenceswhencountispositiveandafterwhennegative,makingitidealforparsingemailaddresses,filepaths,andURLsinMySQLd

Sep 02, 2025 am 02:50 AM

mysql

How to perform an INNER JOIN in SQL

AnINNERJOINreturnsonlyrowswithmatchingvaluesinbothtables;1)UseSELECTtospecifydesiredcolumns;2)UseFROMforthefirsttable;3)UseINNERJOINwiththesecondtable;4)UseONtodefinethejoincondition,typicallymatchingprimaryandforeignkeys;5)Optionally,joinmultipletab

Sep 02, 2025 am 02:39 AM