关键字:sqlserver 2012,FOR XML PATH, 连接字符串 大家可能在工作中都遇到过需要聚合字符串的情况,例如: 实际的表数据如下 depart name 开发部 张三 开发部 李四 财务部 王二 财务部 麻子 运营部 路人甲 然后通过聚合,希望得到的结果 depart name 开发
关键字:sqlserver 2012,FOR XML PATH, 连接字符串
大家可能在工作中都遇到过需要聚合字符串的情况,例如:
实际的表数据如下
depart | name |
开发部 | 张三 |
开发部 | 李四 |
财务部 | 王二 |
财务部 | 麻子 |
运营部 | 路人甲 |
然后通过聚合,希望得到的结果
depart | name |
开发部 | 张三,李四 |
财务部 | 王二,麻子 |
运营部 | 路人甲 |
实际上,有三种方法可以实现这样的结果
1,使用自定义方法(function)
2,使用游标(cursor)
3,使用for xml path函数
这里主要介绍第三种,因为理论上代码的复杂度和开销都相对会小一点。
代码如下
<span>select</span><span> depart, </span><span>[</span><span>name</span><span>]</span><span>=</span><span>stuff</span><span>((</span><span>select</span><span>'</span><span>,</span><span>'</span><span>+</span><span>[</span><span>name</span><span>]</span><span>from</span><span> tb t </span><span>where</span><span> id </span><span>=</span><span> tb.depart </span><span>for</span><span> xml path(</span><span>''</span><span>)) , </span><span>1</span><span> , </span><span>1</span><span> , </span><span>''</span><span>) </span><span>from</span><span> tb </span><span>group</span><span>by</span><span> depart</span>

MySQLstringtypesimpactstorageandperformanceasfollows:1)CHARisfixed-length,alwaysusingthesamestoragespace,whichcanbefasterbutlessspace-efficient.2)VARCHARisvariable-length,morespace-efficientbutpotentiallyslower.3)TEXTisforlargetext,storedoutsiderows,

MySQLstringtypesincludeVARCHAR,TEXT,CHAR,ENUM,andSET.1)VARCHARisversatileforvariable-lengthstringsuptoaspecifiedlimit.2)TEXTisidealforlargetextstoragewithoutadefinedlength.3)CHARisfixed-length,suitableforconsistentdatalikecodes.4)ENUMenforcesdatainte

MySQLoffersvariousstringdatatypes:1)CHARforfixed-lengthstrings,2)VARCHARforvariable-lengthtext,3)BINARYandVARBINARYforbinarydata,4)BLOBandTEXTforlargedata,and5)ENUMandSETforcontrolledinput.Eachtypehasspecificusesandperformancecharacteristics,sochoose

TograntpermissionstonewMySQLusers,followthesesteps:1)AccessMySQLasauserwithsufficientprivileges,2)CreateanewuserwiththeCREATEUSERcommand,3)UsetheGRANTcommandtospecifypermissionslikeSELECT,INSERT,UPDATE,orALLPRIVILEGESonspecificdatabasesortables,and4)

ToaddusersinMySQLeffectivelyandsecurely,followthesesteps:1)UsetheCREATEUSERstatementtoaddanewuser,specifyingthehostandastrongpassword.2)GrantnecessaryprivilegesusingtheGRANTstatement,adheringtotheprincipleofleastprivilege.3)Implementsecuritymeasuresl

ToaddanewuserwithcomplexpermissionsinMySQL,followthesesteps:1)CreatetheuserwithCREATEUSER'newuser'@'localhost'IDENTIFIEDBY'password';.2)Grantreadaccesstoalltablesin'mydatabase'withGRANTSELECTONmydatabase.TO'newuser'@'localhost';.3)Grantwriteaccessto'

The string data types in MySQL include CHAR, VARCHAR, BINARY, VARBINARY, BLOB, and TEXT. The collations determine the comparison and sorting of strings. 1.CHAR is suitable for fixed-length strings, VARCHAR is suitable for variable-length strings. 2.BINARY and VARBINARY are used for binary data, and BLOB and TEXT are used for large object data. 3. Sorting rules such as utf8mb4_unicode_ci ignores upper and lower case and is suitable for user names; utf8mb4_bin is case sensitive and is suitable for fields that require precise comparison.

The best MySQLVARCHAR column length selection should be based on data analysis, consider future growth, evaluate performance impacts, and character set requirements. 1) Analyze the data to determine typical lengths; 2) Reserve future expansion space; 3) Pay attention to the impact of large lengths on performance; 4) Consider the impact of character sets on storage. Through these steps, the efficiency and scalability of the database can be optimized.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function

WebStorm Mac version
Useful JavaScript development tools

MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

Zend Studio 13.0.1
Powerful PHP integrated development environment
