亚洲欧美日韩综合一区在线观看,天堂а√在线地址在线

Article Tags

All
web3.0
- All
- NoSQL database
- Memcached
- cloudera
- memcache
Backend Development
- All
- PHP Tutorial
- Python Tutorial
- Golang
- XML/RSS Tutorial
- C#.Net Tutorial
- C++
- NoSQL database
- Memcached
- cloudera
- memcache
Web Front-end
Database
- All
- Mysql Tutorial
- navicat
- SQL
- Redis
- phpMyAdmin
- Oracle
- MongoDB
- NoSQL database
- Memcached
- cloudera
- memcache
Operation and Maintenance
- All
- Mac OS
- Linux Operation and Maintenance
- Apache
- Nginx
- CentOS
- Docker
- NoSQL database
- Memcached
- cloudera
- memcache
Development Tools
- All
- VSCode
- sublime
- notepad
- git
- composer
- NoSQL database
- Memcached
- cloudera
- memcache
PHP Framework
- All
- Laravel
- YII
- NoSQL database
- Memcached
- cloudera
- memcache
Common Problem
- All
- NoSQL database
- Memcached
- cloudera
- memcache
Other
- All
- IIS
- SEO
- Premiere
- NoSQL database
- Memcached
- cloudera
- memcache
Tech
- All
- AI
- It Industry
- NoSQL database
- Memcached
- cloudera
- memcache
CMS Tutorial
- All
- WordPress
- NoSQL database
- Memcached
- cloudera
- memcache
Java
- All
- javaTutorial
- NoSQL database
- Memcached
- cloudera
- memcache
System Tutorial
- All
- Windows Series
- LINUX
- MAC
- NoSQL database
- Memcached
- cloudera
- memcache
Computer Tutorials
Hardware Tutorial
Mobile Tutorial
- All
- Mobile News
- iPhone
- Android Phone
- NoSQL database
- Memcached
- cloudera
- memcache
Software Tutorial
Mobile Game Tutorial

Home

Technical Articles

Database

SQL

How to sort by a custom order in SQL

Use CASE expressions to implement custom sorting in SQL. 1. Use ORDERBY and CASE to assign sorting weights to each value, which is suitable for all mainstream databases; 2. Use FIELD() function to simplify the syntax in MySQL, but the values ??that are not in the list need to be processed; 3. It is recommended to use ARRAY_POSITION() instead of POSITION() in PostgreSQL to avoid matching errors; 4. For frequently used sorting logic, it is easier to maintain for creating mapping tables and associated queries. This method ensures that the custom order takes effect accurately and supports multi-column sorting and outlier processing, ultimately achieving flexible and reliable sorting results.

Sep 09, 2025 am 02:55 AM

How to disable a trigger in SQL?

InSQLServer,useDISABLETRIGGERtrigger_nameONtable_nametodisableatrigger;2.MySQLlacksdirectsupport,souseauser-definedvariableflaginthetriggerlogicordropandrecreatethetrigger;3.InPostgreSQL,useALTERTABLEtable_nameDISABLETRIGGERtrigger_name;4.InOracle,us

Sep 09, 2025 am 02:45 AM

SQL Server Change Data Capture (CDC) Implementation

To enable SQLServerCDC, follow the steps. First, confirm the version support, and then enable it for the database and table respectively. When querying change data, use built-in functions and LSN ranges. Cleaning up data can be done with default or custom policies. 1. Enable CDC: USEYourDatabaseName; EXECsys.sp_cdc_enable_db; and then enable: EXECsys.sp_cdc_enable_table@source_schema='dbo',@source_name='YourTableName'; 2. Query change: Use cdc.fn_cdc_get_all_chang

Sep 09, 2025 am 02:42 AM

How to concatenate strings in SQL

The use of the CONCAT function is the safest string splicing method across databases. It can automatically treat NULL values ??as empty string processing; this function is supported in MySQL, PostgreSQL, SQLServer, Oracle and SQLite; PostgreSQL, Oracle and SQLite also support splicing using the || operator, where the result of NULL and string splicing is the string itself; SQLServer uses operators, but it should be noted that if any operand is NULL, the result is NULL, so it needs to be used with ISNULL or COALESCE functions to ensure security; in summary, in order to ensure portability and reliability of NULL value processing,

Sep 09, 2025 am 02:22 AM

How to update a table from another table in SQL

ToupdateatableusingdatafromanothertableinSQL,useaJOIN-basedUPDATEsyntaxspecifictoyourdatabasesystem:inMySQL,useUPDATEwithJOIN;inSQLServer,includetheFROMclauseafterSET;inPostgreSQL,useFROMwithWHEREtojoin;alternatively,useasubquerywithWHEREEXISTSforbro

Sep 09, 2025 am 02:21 AM

sql 表更新

How to write a correlated subquery in SQL?

AcorrelatedsubqueryisaSQLsubquerythatdependsontheouterqueryandexecutesonceforeachrowfromtheouterquery.1.Itreferencesacolumnfromtheouterquery,typicallyintheWHERE,SELECT,orHAVINGclause,formingalinkthatmakesit"correlated."2.Example:Findemploye

Sep 09, 2025 am 01:03 AM

SQL Data Loss Prevention (DLP)

SQL Data Leakage Prevention (DLP) is a mechanism to prevent sensitive data such as user information and transaction records in the database from being illegally accessed, exported or deleted. The core lies in controlling internal permissions, identifying data flow, and discovering abnormal operations. 1. SQLDLP is a complete set of mechanisms, including identifying sensitive data, controlling access rights, monitoring data export behavior, automatic alarm or blocking abnormal operations; 2. Implementation methods include data classification and tagging, access control (RBAC/ABAC), database audit, real-time monitoring and alarm, and data desensitization; 3. When deploying, pay attention to policy flexibility, log retention time, application layer control, and periodic update of sensitive data definitions; 4. Recommended tools include Microsoft SQLServer audit Dynamic data mask

Sep 08, 2025 am 06:23 AM

How to handle deadlocks in SQL?

DeadlocksinSQLoccurwhentwoormoretransactionsarewaitingforeachothertoreleaselocksonresources,creatingacyclethatpreventsanyprogress.Whiletheycan'talwaysbeavoidedcompletely,theycanbemanagedeffectively.Here’showtohandl

Sep 08, 2025 am 06:05 AM

sql deadlock

How to add a column to an existing table in SQL?

ToaddacolumntoanexistingtableinSQL,usetheALTERTABLEstatementwiththeADDCOLUMNclause;1.Specifythetablename,2.Definethenewcolumnname,3.Assignadatatype,and4.OptionallyincludeconstraintslikeNOTNULLorDEFAULT;syntaxvariesslightlybydatabase—MySQLandPostgreSQ

Sep 08, 2025 am 05:24 AM

sql 添加列

How to use the OVER clause with PARTITION BY in SQL

PARTITIONBYintheOVERclausedividesrowsintogroupsforwindowfunctionswithoutcollapsingthem,enablingper-rowcalculationswithincategories.ItallowswindowfunctionslikeSUM,RANK,andAVGtooperatewithindefinedpartitions(e.g.,regions),preservingalloriginalrowsandpr

Sep 08, 2025 am 05:18 AM

How to find rows that exist in one table but not another in SQL?

Themostreliablemethodstofindrowsinonetablebutnotanotherare:1.UsingLEFTJOINwithISNULL,whichreturnsallrowsfromthelefttablewherenomatchexistsintherighttable;2.UsingNOTEXISTS,whichiseffectiveforcorrelatedsubqueriesandhandlesNULLsbetter;3.UsingNOTINcautio

Sep 08, 2025 am 04:44 AM

How to rename a table in SQL

To rename SQL tables, different syntaxes need to be used according to the database system: 1. In MySQL, PostgreSQL and SQLite, use ALTERTABLEold_table_nameRENAMETOnew_table_name; 2. In SQLServer, use EXECsp_rename'old_table_name','new_table_name'; before the operation, you need to ensure that you have appropriate permissions, check and update dependent objects such as views or stored procedures. It is recommended to test and back up the data in the development environment before executing to avoid production environment problems.

Sep 08, 2025 am 04:37 AM

How to trim whitespace from a string in SQL

UseTRIM()toremovebothleadingandtrailingwhitespace,LTRIM()forleadingonly,andRTRIM()fortrailingonly;thesefunctionsarewidelysupportedinPostgreSQL,MySQL,Oracle,SQLServer(2017 ),andrecentSQLite,withSQLServerbefore2017requiringLTRIM(RTRIM())andsomedatabase

Sep 08, 2025 am 01:36 AM

sql String processing

How to use the ROW_NUMBER function in SQL

ROW_NUMBER()assignsauniquesequentialnumbertoeachrowwithinaresultsetbasedonthespecifiedorder,anditcanalsorestartnumberingwithingroupsusingPARTITIONBY.1.Toassignsequentialnumberstoallrows,useROW_NUMBER()OVER(ORDERBYcolumn)torankrowsuniquely,evenwithdup

Sep 08, 2025 am 01:33 AM