数据库表有3列，Id,Name,ParentId,已从数据库读出数据，如何递归成一棵树

数据库是什么数据库

我先假设你是 Oracle 吧。

CREATE TABLE test_tree (

test_id INT NOT NULL,

pid INT,

test_val VARCHAR(10),

PRIMARY KEY (test_id)

);

INSERT INTO test_tree VALUES(1, NULL, 'NET');

INSERT INTO test_tree VALUES(2, 1, 'C#');

INSERT INTO test_tree VALUES(3, 1, 'J#');

INSERT INTO test_tree VALUES(4, 1, 'ASPNET');

INSERT INTO test_tree VALUES(5, 1, 'VBNET');

INSERT INTO test_tree VALUES(6, NULL, 'J2EE');

INSERT INTO test_tree VALUES(7, 6, 'EJB');

INSERT INTO test_tree VALUES(8, 6, 'Servlet');

INSERT INTO test_tree VALUES(9, 6, 'JSP');

INSERT INTO test_tree VALUES(10, NULL, 'Database');

INSERT INTO test_tree VALUES(11, 10, 'DB2');

INSERT INTO test_tree VALUES(12, 10, 'MySQL');

INSERT INTO test_tree VALUES(13, 10, 'Oracle');

INSERT INTO test_tree VALUES(14, 10, 'SQL Server');

INSERT INTO test_tree VALUES(15, 13, 'PL/SQL');

INSERT INTO test_tree VALUES(16, 15, 'Function');

INSERT INTO test_tree VALUES(17, 15, 'Procedure');

INSERT INTO test_tree VALUES(18, 15, 'Package');

INSERT INTO test_tree VALUES(19, 15, 'Cursor');

INSERT INTO test_tree VALUES(20, 14, 'T-SQL');

使用 START WITH CONNECT BY 语句实现树状查询

通过根节点 向下查询子节点

SELECT

LPAD(' ', 2(LEVEL-1)) || test_val AS test_val

FROM

test_tree

START WITH

test_id IN (1, 6, 10)

CONNECT BY PRIOR test_id = pid;

TEST_VAL

-----------------------------------------------------------

NET

C#

J#

ASPNET

VBNET

J2EE

EJB

Servlet

JSP

Database

DB2

TEST_VAL

-----------------------------------------------------------

MySQL

Oracle

PL/SQL

Function

Procedure

Package

Cursor

SQL Server

T-SQL

20 rows selected

import javautilArrayList;

import javautilIterator;

import javautilList;

import orgdom4jDocument;

import orgdom4jDocumentException;

import orgdom4jElement;

import orgdom4jioSAXReader;

import orgdom4jtreeDefaultAttribute;

/

Java递归遍历XML所有元素

@author Administrator

@version [版本号, Apr 13, 2010]

@see [相关类/方法]

@since [产品/模块版本]

/

public class XmlParser

{

// private static Map xmlmap = new HashMap();

//存储xml元素信息的容器

private static ArrayList<Leaf> elemList = new ArrayList<Leaf>();

public static void main(String args[])

throws DocumentException

{

XmlParser test = new XmlParser();

String path = "C:/axml";

// 读取XML文件

SAXReader reader = new SAXReader();

Document doc = readerread(path);

// 获取XML根元素

Element root = docgetRootElement();

testgetElementList(root);

String x = testgetListString(elemList);

Systemoutprintln("-----------解析结果------------\n" x);

}

用标准sql的with实现递归查询（sql2005以上肯定支持，sql2000不清楚是否支持）：

with subqry(id,name,pid) as (

select id,name,pid from test1 where id = 5

union all

select test1id,test1name,test1pid from test1,subqry

where test1pid = subqryid

)

select from subqry;

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