Oracle同行合并分组
Oracle同行合并分组，使用函数sys_connect_by_path(column,
Oracle同行合并分组
使用函数sys_connect_by_path(column,'')的例子^^。
表结构为：
create table test(
bookid char(3) not null,
author varchar2(10) not null
);
insert into test values('001','jack');
insert into test values('001','tom');
insert into test values('002','wang');
insert into test values('002','zhang');
insert into test values('002','li');
commit;
select * from test;
显示结果为：
BOO AUTHOR
-----------------
001 jack
001 tom
002 wang
002 zhang
002 li
我们想得到的结果为：
BOO AUTHOR
-----------------------------
001 jack&&tom
002 wang&&zhang&&li
SQL文为：
select bookid,substr(max(sys_connect_by_path(author,'&&')),3) author
from
(select bookid,author,id,lag(id) over(partition by bookid order by id) pid
--(最后一列或者为)lead(id) over(partition by bookid order by id desc) pid
from (select bookid,author,rownum id from test))
start with pid is null
connect by prior id=pid
group by bookid;
详细解释：
sys_connect_by_path(column,'')//column为列名，''中间加要添加的字符
这个函数本身不是用来给我们做结果集连接的（合并行），，而是用来构造树路径的，所以需要和connect by一起使用。
test只是张普通表，怎样才能变成树结构呢？我们需要加一个pid和id。
id我们只需加一个rownum就好。
select bookid,author,rownum id from test;
BOO AUTHOR ID
----------------------------
001 jack 1
001 tom 2
002 wang 3
002 zhang 4
002 li 5
而pid上一条记录不就是下一条记录的父节点了。这里我们需要函数lag()取前记录，和lead()相对。
//把lag(id) over(order by id) pid改成lead(id) over(order by id desc) pid效果一样
select bookid,author,id,lag(id) over(order by id) pid
from (select bookid,author,rownum id from test);
BOO AUTHOR ID PID
-------------------------------------------
001 jack 1
001 tom 2 1
002 wang 3 2
002 zhang 4 3
002 li 5 4
由于要按bookid分我们的pid，在分析函数over中我们需要加上partition by，一看下面结果我们就知道有什么不同了。
select bookid,author,id,lag(id) over(partition by bookid order by id) pid
from (select bookid,author,rownum id from test);
BOO AUTHOR ID PID
-------------------------------------------
001 jack 1
001 tom 2 1
002 wang 3
002 zhang 4 3
002 li 5 4
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
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1662
14
1419
52
1311
25
1261
29
1234
24
iOS 18 adds a new 'Recovered' album function to retrieve lost or damaged photos
Jul 18, 2024 am 05:48 AM
Apple's latest releases of iOS18, iPadOS18 and macOS Sequoia systems have added an important feature to the Photos application, designed to help users easily recover photos and videos lost or damaged due to various reasons. The new feature introduces an album called "Recovered" in the Tools section of the Photos app that will automatically appear when a user has pictures or videos on their device that are not part of their photo library. The emergence of the "Recovered" album provides a solution for photos and videos lost due to database corruption, the camera application not saving to the photo library correctly, or a third-party application managing the photo library. Users only need a few simple steps
MySQL: Simple Concepts for Easy Learning
Apr 10, 2025 am 09:29 AM
MySQL is an open source relational database management system. 1) Create database and tables: Use the CREATEDATABASE and CREATETABLE commands. 2) Basic operations: INSERT, UPDATE, DELETE and SELECT. 3) Advanced operations: JOIN, subquery and transaction processing. 4) Debugging skills: Check syntax, data type and permissions. 5) Optimization suggestions: Use indexes, avoid SELECT* and use transactions.
Top 10 global digital currency trading apps recommended (2025 currency trading software ranking)
Mar 12, 2025 pm 05:48 PM
This article recommends the top ten digital currency trading apps in the world, including Binance, OKX, Huobi Global, Coinbase, Kraken, Gate.io, KuCoin, Bitfinex, Gemini and Bitstamp. These platforms have their own characteristics in terms of transaction pair quantity, transaction speed, security, compliance, user experience, etc. For example, Binance is known for its high transaction speed and extensive services, while Coinbase is more suitable for novices. Choosing a platform that suits you requires comprehensive consideration of your own needs and risk tolerance. Learn about the world's mainstream digital currency trading platforms to help you conduct digital asset trading safely and efficiently.
How to install and register the btc trading app?
Feb 21, 2025 pm 07:09 PM
This article will provide a detailed introduction to how to install and register a Bitcoin trading application. The Bitcoin trading app allows users to manage and trade cryptocurrencies such as Bitcoin. The article guides users through the installation and registration process step by step, including downloading applications, creating accounts, performing identity verification, and first deposit. The goal of the article is to provide beginners with clear and easy-to-understand guidelines to help them easily enter the world of Bitcoin trading.
MySQL: An Introduction to the World's Most Popular Database
Apr 12, 2025 am 12:18 AM
MySQL is an open source relational database management system, mainly used to store and retrieve data quickly and reliably. Its working principle includes client requests, query resolution, execution of queries and return results. Examples of usage include creating tables, inserting and querying data, and advanced features such as JOIN operations. Common errors involve SQL syntax, data types, and permissions, and optimization suggestions include the use of indexes, optimized queries, and partitioning of tables.
Ouyi Exchange Download Official Portal
Feb 21, 2025 pm 07:51 PM
Ouyi, also known as OKX, is a world-leading cryptocurrency trading platform. The article provides a download portal for Ouyi's official installation package, which facilitates users to install Ouyi client on different devices. This installation package supports Windows, Mac, Android and iOS systems. Users can choose the corresponding version to download according to their device type. After the installation is completed, users can register or log in to the Ouyi account, start trading cryptocurrencies and enjoy other services provided by the platform.
Why Use MySQL? Benefits and Advantages
Apr 12, 2025 am 12:17 AM
MySQL is chosen for its performance, reliability, ease of use, and community support. 1.MySQL provides efficient data storage and retrieval functions, supporting multiple data types and advanced query operations. 2. Adopt client-server architecture and multiple storage engines to support transaction and query optimization. 3. Easy to use, supports a variety of operating systems and programming languages. 4. Have strong community support and provide rich resources and solutions.
Oracle's Role in the Business World
Apr 23, 2025 am 12:01 AM
Oracle is not only a database company, but also a leader in cloud computing and ERP systems. 1. Oracle provides comprehensive solutions from database to cloud services and ERP systems. 2. OracleCloud challenges AWS and Azure, providing IaaS, PaaS and SaaS services. 3. Oracle's ERP systems such as E-BusinessSuite and FusionApplications help enterprises optimize operations.
